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Plants: an international scientific open access journal to publish all facets of plants, their functions and interactions with the environment and other living organisms.

Introduction

Plants as a source of food:, the environmental impact:, biodiversity:, references and notes.

• Bennett, B.C. Plants as Food. Bennett, Brad, Ed.; Developed under the Auspices of the UNESCO; Eolss Publishers: Oxford, UK, 2010. [ Google Scholar ]
• Zeenews.com. Available online: http://zeenews.india.com/sci-tech/ecology/index26.html (accessed on 25 January 2012).
• Planetsave. Available online: http://planetsave.com/2011/05/20/endangered-plants-list/ (accessed on 16 January 2012).

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Fernando, W.G.D. Plants: An International Scientific Open Access Journal to Publish All Facets of Plants, Their Functions and Interactions with the Environment and Other Living Organisms. Plants 2012 , 1 , 1-5. https://doi.org/10.3390/plants1010001

Fernando WGD. Plants: An International Scientific Open Access Journal to Publish All Facets of Plants, Their Functions and Interactions with the Environment and Other Living Organisms. Plants . 2012; 1(1):1-5. https://doi.org/10.3390/plants1010001

Fernando, W.G. Dilantha. 2012. " Plants: An International Scientific Open Access Journal to Publish All Facets of Plants, Their Functions and Interactions with the Environment and Other Living Organisms" Plants 1, no. 1: 1-5. https://doi.org/10.3390/plants1010001

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• Published: 01 April 2021

Research advances in and prospects of ornamental plant genomics

• Tangchun Zheng 1 ,
• Ping Li 1 ,
• Lulu Li 1 &
• Qixiang Zhang 1  

Horticulture Research volume  8 , Article number:  65 ( 2021 ) Cite this article

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• DNA sequencing
• Plant genetics

The term ‘ornamental plant’ refers to all plants with ornamental value, which generally have beautiful flowers or special plant architectures. China is rich in ornamental plant resources and known as the “mother of gardens”. Genomics is the science of studying genomes and is useful for carrying out research on genome evolution, genomic variations, gene regulation, and important biological mechanisms based on detailed genome sequence information. Due to the diversity of ornamental plants and high sequencing costs, the progress of genome research on ornamental plants has been slow for a long time. With the emergence of new sequencing technologies and a reduction in costs since the whole-genome sequencing of the first ornamental plant ( Prunus mume ) was completed in 2012, whole-genome sequencing of more than 69 ornamental plants has been completed in <10 years. In this review, whole-genome sequencing and resequencing of ornamental plants will be discussed. We provide analysis with regard to basic data from whole-genome studies of important ornamental plants, the regulation of important ornamental traits, and application prospects.

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Introduction.

Genomics is the science of studying genomes. It is used to summarize a branch of genetics involving genome mapping, sequencing, and whole-genome functional analysis. The whole genome is taken as the research object, with a focus on analyzing all of the genetic information in whole genomes of organisms. The main purpose of carrying out genomics research is to interpret the whole-genome sequence, including genomic variations and gene regulation, through mining and expression to gain a deeper understanding of biological mechanisms, formulate more effective breeding strategies, expand the mining breadth and depth of excellent alleles in germplasm resources, and increase the operability for improving complex traits and the efficiency of breeding new varieties.

Ornamental plants, a vital component of agriculture and horticulture, are of great significance for beautifying and improving humans’ living environment, cultivating human sentiment, and promoting structural adjustments in the agricultural industry. The first plant genome to be published was that of Arabidopsis thaliana in 2000 1 . With the emergence of next-generation and high-throughput sequencing, sequencing technologies have continuously evolved, while their costs have continuously decreased, facilitating the whole-genome sequencing of many plants. According to incomplete statistics, whole-genome sequencing has been completed for ~400 plants 2 . With this progress, more abundant genetic data are provided for plant diversity studies, enabling breeders to perform comprehensive multidimensional research in the fields of genetics, genomics, and molecular breeding. This brings new development opportunities and driving forces for the breeding of more plants and thus leads to a new revolution of breeding technology. Since genome sequencing of the first ornamental plant ( Prunus mume ) was completed in 2012 3 , whole-genome sequencing of more than 65 ornamental plants has been completed in <10 years. The whole-genome sequencing results from these ornamental plant species have built an enormous resource platform for molecular biology research in ornamental horticulture, which not only contributes to the understanding of genome structure and function in ornamental horticulture but also has substantial guiding significance for exploring the origin and evolution of ornamental plants, mapping and cloning the functional genes of important traits and accelerating the course of molecular breeding.

In this study, the research results from whole-genome sequencing and resequencing of ornamental plants are summarized. We provide a discussion with regard to basic data from whole-genome studies of important ornamental plants, the regulation of important ornamental traits, and application prospects.

Whole-genome sequences of ornamental plants

As of 30 October 2020, the whole-genome sequences and draft genome sequences of 69 ornamental plants have been published, including herbaceous plants, such as carnation ( Dianthus caryophyllus ), phalaenopsis ( Phalaenopsis aphrodite ), orchid ( Apostasia odorata ), sacred lotus ( Nelumbo nucifera ), chrysanthemum ( Dendranthema morifolium ) and Dionaea muscipula , and woody plants, such as mei ( Prunus mume ), Yoshino cherry ( Prunus yedoensis ), sweet osmanthus ( Osmanthus fragrans ), peony ( Paeonia suffruticosa ), and Chinese rose ( Rosa chinensis ) (Table 1 ). The number of sequenced genomes of ornamental plants completed each year significantly increased from 1 in 2012 to 17 in 2018. In particular, more than 10 species were sequenced for three consecutive years from 2016 to 2018 (Fig. 1a ). China has independently completed or led genome sequencing for 32 ornamental plants, followed by Japan and the United States, which have also completed the genome sequencing of more than 10 species (Fig. 1b ). Considering the sequencing material, except for the double-haploid material with relatively high homozygosity used for R. chinensis 4 , 5 , wild diploids or cultivars with relatively unclear genetic backgrounds and low heterozygosity were used for all of the other plants. Long-read sequencers in combination with optical maps 6 are used to generate high-quality chromosome-level genome assemblies. For ornamental plants, the PacBio RS II system was first applied for the construction of the 1.27 Gb genome assembly of Dendrobium officinale 7 . Long-range scaffolding techniques such as high-throughput chromosome conformation capture (Hi-C) facilitate chromosome-scale assembly of contigs. In this respect, recently built genome assemblies of Rosa chinensis (515 Mb) have a contig N50 of 24 Mb, which is one of the most comprehensive plant genomes 4 . In consideration of the comprehensive utilization of Illumina HiSeq, Nanopore, PacBio, and Hi-C technologies, the contig N50 values of Gardenia jasminoides and Chimonanthus praecox can reach 44 and 65.35 Mb, respectively, which was unthinkable five years ago 8 , 9 . Generally, the sequencing technology that is predominantly used is next-generation sequencing on the Illumina platform (HiSeq 2000/2500/4000 and HiSeq X ten), coupled with third-generation sequencing (PacBio and Nanopore) and Hi-C technology. The assembled genome size of sequenced ornamental plants ranges from 237 Mb to 13.79 Gb with a scaffold N50 ranging from 13.8 Kb to 65.35 Mb (Fig. 2 ). We constructed phylogenetic trees for all species with a published genome, which belong to 21 orders and 35 families (Fig. 3 ). The representative species in Rosaceae, Orchidaceae, and Asteraceae for which high-quality sequencing has been completed were described and discussed.

a Distribution of genome sequencing for ornamental plants completed from 2012 to 2020; b Distribution of genome sequencing for ornamental plants completed in different countries

The x -axis represents the genome size of each plant, while the y -axis shows the scaffold N50 of the genome assembly. The sequencing platforms are indicated in different colors

A maximum likelihood (ML) phylogenetic tree was built using low-copy orthologous sequences. All the published ornamental species belong to 21 orders and 35 families. The same background color was used for species in the same family

Rosaceae contains more than 3300 species in 124 genera that are rich in economic and ornamental value and occupy an important position in gardens worldwide. The first flowering ornamental plant to be sequenced was Prunus mume (mei) from Rosaceae. In 2009, the National Engineering Research Center for Floriculture of Beijing Forestry University cooperated with the Beijing Genomics Institute (BGI) and other institutions to launch the mei genome project. First, a 237 Mb (84.6% of the estimated genome) genome of wild-type mei was assembled using the Illumina GA II. The scaffold N50 was 577.8 Kb, and 31,390 protein-coding genes were annotated. The genome data were published in Nature Communications in 2012, and this effort marked the first genome sequence map of a flowering crop worldwide 3 . Interestingly, equal to the status of mei in China, the “Yoshino cherry” tree ( Prunus × yedoensis ) is one of the most popular Prunus species in Japan, and its genome was sequenced by Korean researchers, revealing the parental origin and genomic delimitation of hybrid taxa using both Illumina and PacBio platforms in 2018 10 . Soon afterwards, researchers from Japan also completed two similar genomes of Cerasus yedoensis , “Somei-Yoshino”, which were merged into a special genome 11 . At present, a large number of genome studies focusing on Prunus and Rosa in Rosaceae are underway.

Roses have high cultural and economic value as the most commonly cultivated ornamental and spice plants worldwide. The first ornamental Rosa to have its genome sequenced was Rosa multiflora , which was reported by Japanese scholars focusing on flower color, flower scent, and floral development traits 12 . Then, another well-known and long-awaited major study was published in Nature Genetics in May 2018. A team at the University of Lyon and Centre National de la Recherche Scientifique (CNRS) first revealed another parent of the modern rose, Rosa chinensis . The size of the Rosa genome is 560 Mb with a contig N50 of 24 Mb, which is one of the most comprehensive plant genomes 4 . Coincidentally, one month later, the same experimental material (a doubled haploid line from ‘Old Blush’) of Rosa chinensis was sequenced and republished in Nature Plants in June 2018. The high-quality genome was cross-verified, and ornamental and production traits of rose have been interpreted with the joint efforts of many research institutions from France, Belgium, Russia, etc. 5 .

Orchidaceae

As one of the most abundant families in the plant kingdom, Orchidaceae (orchid) plants are the flagship species of plant diversity protection, known as the “panda of the plant kingdom”. Orchids are divided into five subfamilies: Apostasioideae, Vanilloideae, Cypripedioideae, Orchidoideae, and Epidendroideae. Phalaenopsis and Dendrobium belong to Orchidoideae and Epidendroideae. Phalaenopsis plants are representative of Orchidaceae plants and have important ornamental value. Professor Zhongjian Liu of the National Orchid Conservation Center of China overcame technical problems resulting from high heterozygosity and completed the assembly of the whole-genome sequence of P. equestris with a scaffold N50 size of 359.1 Kb. As the first monocot flower for which genome-wide sequencing was completed, the genome of P. equestris was published as a cover paper in the journal Nature Genetics in November 2014 13 . Phalaenopsis is an important potted flower with high economic value worldwide. A 3.1 Gb draft genome assembly of an important winter-flowering Phalaenopsis cultivar ‘KHM190’ was completed by researchers from China and Australia 14 . Another species of Phalaenopsis , P. aphrodite , also underwent high-quality genome sequencing with a scaffold N50 size of 19.7 Mb in April 2018 15 . Scholars from China further analyzed the whole genomes of Dendrobium officinale and Dendrobium catenatuma , which were published in the journals Molecular Plant and Scientific Reports , respectively 7 , 16 . Apostasia shenzhenica is representative of one of two genera that form a sister lineage with the rest of the Orchidaceae ; they have unique flower morphologies as well as diverse lifestyles and habitats. Professor Zhongjian Liu resequenced the high-quality genome of A. shenzhenica with a scaffold N50 size of 3.0 Mb. A 349 Mb genome was assembled and published in Nature in 2017 17 . Vanilla fragrans is a plant of the vanilla family. Due to its unique fragrance that cannot be synthesized artificially, it is known as the “Perfume Queen”. In July 2014, the Fujian Agriculture & Forestry University and National Orchid Conservation Center of China (Shenzhen) officially launched the Vanilla shenzhenica genome project. As the first Orchidaceae vine plant to undergo complete sequencing, the genome of V. shenzhenica was ~800 Mb with a scaffold N50 size of 288 Kb, and its heterozygosity was ~1.14% ( https://www.fafu.edu.cn/2015/0208/c132a18466/page.htm ).

There are ~24,000–35,000 species in Asteraceae; this family has very high plant diversity, accounting for ~10% of total angiosperms. Chrysanthemum , as a typical representative genus, is one of the most important ornamental crops in the world. The genome of Chrysanthemum morifolium is estimated to be more than 9 Gb ( http://data.kew.org/cvalues/ ). Since the Chrysanthemum genus is large and complex, the genome of Chrysanthemum was not reported for a long time. In October 2018, the China Academy of Chinese Medical Sciences, Hubei University of Chinese Medicine cooperated with Nanjing Agricultural University and completed the sequencing of Chrysanthemum nankingense , a diploid species (2 n  = 18), which represents one of the progenitor genomes of domesticated chrysanthemums 18 . At around the same time, the de novo whole-genome assembly of Chrysanthemum seticuspe was announced by researchers from the Kazusa DNA Research Institute of Japan 19 . The 2.72 Gb of assembled sequences covered 89.0% of the 3.06 Gb  C. seticuspe genome with 71,057 annotated genes 19 . Sunflower ( Helianthus annuus L.), in the Asteraceae and the Helianthus genus, is a horticultural crop with important economic and ornamental value and a major research focus. In May 2017, a high-quality reference for the sunflower genome was published in the journal Nature by scientists from France and Canada 20 . The size of the sunflower genome was 2.94 Gb and covered 80% of the estimated genome; finally, 97% of annotated genes were anchored on a total of 17 pseudochromosomes.

Resequencing of ornamental plants

Whole-genome resequencing is a process of sequencing the genomes of different individuals of species with known genome sequences and analyzing the differences among individuals or populations. In recent years, to overcome the narrow genetic variation in current ornamental plant breeding programs, genome-scale investigations of wide germplasm panels and cultivated varieties have served to identify important genetic materials to study genomic variation dynamics during domestication and selective breeding 71 . For example, resequencing of multiple materials from different crop species based on genome-wide association study (GWAS) was facilitated to identify key genomic regions associated with plant domestication and selection/improvement 72 . Based on genome-wide resequencing technology, researchers can quickly screen resources, find a large number of genetic variations, and realize genetic evolution analysis and prediction of important candidate genes. Although great progress has been made in the de novo sequencing of ornamental plant genomes, only a few species of ornamental plants, such as sunflower, lotus, mei, rose, sakura, and Liriodendron chinense , have undergone genome resequencing (Table 2 ).

Sunflower is not only an ornamental plant but also one of the four major oil crops in the world. In June 2017, genome sequencing of sunflower was completed, eighty domesticated lines (10–20× coverage) and 72 inbred lines (9.3–19.5× coverage) from 480 F 1 hybrids were resequenced, and 35 genomic regions associated with flowering time were identified by GWAS 20 . Subsequently, to characterize genetic diversity in sunflower and to quantify contributions from wild relatives, scientists from the University of British Columbia sequenced 493 accessions, including cultivars, landraces, and wild relatives 73 . In all, 61,205 genes have been identified within the gene set of the sunflower pangenome, and a large number of candidate resistance genes and single nucleotide polymorphism (SNP) markers for downy mildew resistance were identified by GWAS, which may be of interest to other researchers and sunflower breeders 73 .

To reveal the evolutionary history of Prunus mume and the Prunus genus and the genetic mechanism of important ornamental characteristics of P. mume , 333 cultivated landraces, 15 wild P. mume , and three close relatives of Prunus ( P. sibirica , P. davidiana , and P. salicina ) were selected for genome-wide resequencing by Professor Qixiang Zhang from the National Engineering Research Center for Floriculture of China 74 . A total of 5.34 million high-quality SNPs were identified, and 24 important ornamental traits (such as petal color, stigma color, calyx color, bud color, stamina filament color, wood color, petal number, pistil character, bud aperture, and branching phenotype) of 333 cultivars of P. mume were analyzed by GWAS for the first time to confirm the hypothesis that P. mume exists due to introgression from P. sibirica and P. salicina 74 .

Three versions of the lotus genome have been published in five years 21 , 24 , 50 . To explore the genomic diversity and microevolution related to the rhizome growth pattern, especially the genomic markers of ecotype differentiation, researchers from the Wuhan Botanical Garden of the Chinese Academy of Sciences resequenced 19 individuals including rhizome lotus, seed lotus, flower lotus, wild lotus, Thai lotus and Nelumbo lutea 75 . Candidate genes associated with temperate and tropical lotus divergence always exhibited highly divergent expression patterns, which are valuable for the breeding and cultivation of lotus 75 .

Roses have high cultural and economic value because of their outstanding ornamental characteristics and essential oil composition. To analyze the genetic diversity and genetic regulation mechanism of important ornamental traits in roses, eight Rosa species representing three of the four subgenera ( R. persica , R. minutifolia and Rosa ) were resequenced, and the whole-genome sequence of a double-haploid rose line was completed 5 . At the same time, to gain insight into the makeup of modern roses, Raymond et al. 4 resequenced representatives of three sections (“Synstylae”, “Chinenses” and “Cinnamomeae”) that participated in the domestication and breeding of the modern hybrid rose after the genome of homozygous Rosa chinensis ‘Old Blush’ was sequenced.

Sakura ( Prunus yedoensis ) is a woody ornamental plant with important cultural and economic value. To study the genomic relationship between P. yedoensis and its closely related species, nine P. yedoensis accessions and seven accessions of candidate parental species, including P. pendula , P. jamasakura and P. sargentii , were resequenced and compared to the assembled genome by researchers from Korea 10 . Resequencing data of six related taxa show that 41% of the genes were assigned to the parent state, suggesting that wild P. yedoensis is an F 1 hybrid originating from a cross between P. pendula and P. jamasakura 10 .

Liriodendron chinense is an important woody ornamental plant known as a “woody tulip” in the UK and USA, as its flower shape is similar to that of the tulip. The high-quality genome of L. chinense was published in the journal Nature Plants in December 2018 in a project led by Professor Jisen Shi from Nanjing Forestry University 57 . To explore the historical demographic fluctuations and present-day genetic diversity between L. chinense and L. tulipifera , 14 L. chinense individuals and 6  L. tulipifera individuals were resequenced. Population analysis showed that Liriodendron can be divided into three subgroups: the Eastern China subgroup, Western China subgroup and North American subgroup. The species divergence time confirmed that the genetic diversity of L. chinense was much higher than that of L. tulipifera 57 .

Applications of whole-genome sequencing in ornamental plants

Gene annotation.

Gene annotation is the process of attributing biological information to the completed sequence of a species using bioinformatics methods. It identifies gene fragments that do not encode proteins, recognizes elements on genes (gene prediction) and adds biological information to the elements for sequence repeat identification, noncoding RNA prediction, gene structure prediction, and gene function annotation. In this way, genes associated with ornamental horticultural traits such as flowering regulation, flower color, floral fragrance, plant type, dormancy, cold resistance, and disease resistance can be identified. The dormancy-associated MADS-box transcription factor (DAM) family, which is related to dormancy induction and release, is especially critical for ornamental plants 76 . Zhang et al. 3 identified six DAM genes in the tandem array in the P. mume genome and confirmed that the distribution pattern was consistent with that from previous studies of the peach genome 77 . In Rosa , Raymond et al. 4 identified new candidate genes potentially involved in recurrent blooming, such as TFL1 , SPT , and DOG1 .

Comparative genomics research

Based on genome mapping and sequencing technologies, comparative genomics research compares known genes and genome structures to understand the functions of associated genes, their expression mechanism, and the phylogenetic relationships of species. The acquisition of genomic information from multiple closely related species facilitates more comprehensive and in-depth research in comparative genomics. Moreover, it is crucial to perform in-depth comparative analysis of the collinear relationship between the genome sequences of two plants to analyze the origin and evolutionary relationship of plants and to explore important chromosome fragments or gene clusters that control major plant traits, which can provide essential reference information for the discovery and cloning of important genes. Zhang et al. constructed nine ancestral chromosomes of the Rosaceae family by comparing Rosaceae genomes. For the first time, these researchers revealed that ancestral chromosomes have evolved into eight existing chromosomes in P. mume via 11 fusions, seven existing chromosomes in strawberry ( Fragaria ananassa ) via 15 fusions and 17 existing chromosomes in apple ( Malus domestica ) via one whole-genome duplication event plus five fusions. These findings lay an important foundation for research to unravel the origin and evolution of Rosaceae 3 .

Resequencing

Whole-genome resequencing involves the sequencing of genomes in different individuals of species with known genome sequences and subsequent analysis of differences among individuals or populations. Whole-genome resequencing technology can be used to rapidly conduct resource screening, to find a large number of genetic variations and to implement genetic evolution analysis and candidate gene prediction for important traits. These results provide essential references for identifying valuable genetic resources and for horticultural crop breeding and are thus of significant research and industrial value. In P. mume , researchers investigated the genetic architecture of floral traits and plant domestication history by resequencing 348 P. mume accessions and three other Prunus species at an average sequencing depth of 19.3×. Highly admixed population structure and introgression from Prunus species were identified in mei accessions 74 . Huang et al. 75 resequenced and analyzed the genomes of 19 lotus germplasms, provided a reliable and detailed understanding of the genome evolution of different lotus germplasms, and provided clues to key mutations responsible for rhizome enlargement.

A GWAS is a genome-wide comparative analysis or correlation analysis using millions of SNPs in the genome as molecular genetic markers. It is a new strategy to find genetic variations that affect complex traits by comparison. With the development of genomics research and DNA microarray technology, a GWAS can provide an outlined overview of important traits simultaneously and is therefore suitable for the study of complex traits. At the genome-wide level, association studies between genes and traits are conducted with multiple centers, large samples, and repeated verifications. This method has been applied for the screening and identification of major genes for important economic traits in agriculture. In P. mume , through a GWAS, researchers have identified significant quantitative trait loci (QTLs) and genomic regions where several genes associated with petal color, stigma color, calyx color, bud color, stamina filament color, wood color, petal number, pistil character, bud aperture, and branching phenotype are located 74 . Taken together, the identification of genetic loci associated with floral and other traits provides more insight into the genetic mechanisms that underlie the domestication of P. mume and provides opportunities to design strategies for genomic selection to improve the performance of ornamental species. In sunflowers and roses, the key ornamental trait of flowering time was also identified by the GWAS method 4 , 20 .

Comparative analysis with transcriptome data

RNA sequencing is a newly emerging technology that uses next-generation sequencing for transcriptome analysis. It can comprehensively and rapidly acquire sequence information and expression information for almost all transcripts from specific cells or tissues in a particular state, including protein-coding mRNAs and various noncoding RNAs, as well as the expression abundance of different transcripts generated by alternative gene splicing. The transcriptome is an inevitable link that connects genetic information of the genome with the biological functions of the proteome. Currently, transcriptional regulation is the most well-studied and foremost regulatory method in organisms. Transcriptome studies are the foundation and starting point of gene function-structure studies and the first issue to address after the completion of whole-genome sequencing. Furthermore, transcriptome analysis provides large numbers of molecular markers, such as simple sequence repeats and SNPs. All of the sequence information, expression data, and molecular markers facilitate the localization of QTLs for key ornamental traits in ornamental plants through genetic mapping and contribute to the development of molecular markers in close linkage with excellent traits for use in the molecular marker-assisted breeding of flowers. Based on the genome sequence of P. mume , vital differences in gene expression between the bud stage and squaring stage were observed, and 7,813 DEGs were identified, which provided a special perspective on floral scent formation in P. mume 78 . The water lily genome revealed variable genomic signatures of ancient vascular cambium losses, and the expression profiles of floral ABCE genes, floral scent and color genes were screened from the DEGs in a comparative analysis of the transcriptome 64 .

Development of SNP microarrays

According to their position in genes, SNPs can occur in coding regions, noncoding regions, and gene spacer regions. They are DNA molecular markers that have the most abundant polymorphisms in the genome and are characterized by large numbers, a uniform distribution, and easy typing. SNPs can be used for the identification of genetic variation and genotyping of associated phenotypes. Using SNPs as molecular markers to construct genetic variation maps of the genome has become a vital part of the research for studying genome diversity, obtaining domesticated selection regions, and screening key genes of important traits. Based on the genome sequence and resequencing of P. mume , a total of 1,298,196 raw SNPs were located within coding regions of genes, 733,292 of which were nonsynonymous 74 . Furthermore, by combining transcriptome data, 76 SNPs within DEGs were identified that were associated with petal, stigma, calyx, and bud color 74 . In sacred lotus , wild and Thai lotus exhibited greater differentiation with a higher genomic diversity than cultivated lotus based on SNP sites in resequenced species 75 .

Exploiting genes associated with important ornamental traits

During the course of whole-genome sequencing, a very large number of genes, in the range of 19,507–87,603, are annotated for each flowering species (Table 1 ). Through further analysis, important genes associated with floral development, flower color formation, and stress resistance can be discovered. This is conducive to the breeding of unique, high-quality, and high-resistance varieties or types of a species and provides important references for improving ornamental and resistance qualities in other flowering species.

Candidate genes for controlling floral development

Flower blooming is a process that involves the formation of inflorescence meristems and flower meristem tissues through floral induction and a series of internal and external factors, followed by the generation of floral organ primordia and eventually the release of flora bud dormancy to form floral organs. The process of flowering is controlled by a complex regulatory network, with at least seven flowering regulation pathways found in A. thaliana 79 . The genes associated with floral development can be divided into two classes. One class consists of genes that control the formation of inflorescence meristems and determine the direction of newly formed floral primordia. These genes influence the flowering time of plants by controlling the formation of inflorescence meristems or flower meristems, and mutations in these genes can result in earlier or later flowering mutants. The other class consists of genes that determine the formation of floral organs, and mutations in these genes can result in homeoboxes 79 . In ornamental plants, the morphology and number of floral organs have undergone substantial variations, for example, double petals, multiple sepals, and multiple pistils and stamens, developing into independent flowers during the course of long-term artificial domestication and cultivation. These variations increase the ornamental value of ornamental plants while providing excellent materials for the study of floral organ development in plants. With genomic data analysis, as an important scientific issue, some key genes related to flowering transition and flower development have been analyzed, such as those in Tarenaya hassleriana 23 , Dendrobium officinale 7 , Primula veris 28 , Dendrobium catenatum 16 , Hibiscus syriacus 41 , Rosa 4 , 5 , 12 , Chrysanthemum 18 , 19 , and Nymphaea colorata 64 .

Candidate genes for controlling anthocyanin synthesis

Flower color is one of the most vital quality traits of ornamental plants. Anthocyanin is an essential pigment for coloring flowers, and its biosynthesis is catalyzed by a series of enzymes 80 . Various anthocyanins are formed due to differences in the substituent groups at varied positions on the basic skeleton, thus leading to different plant organ colors, such as red, purple, blue-purple, and blue. Anthocyanins are flavonoid secondary metabolites in plants and the most widely distributed water-soluble pigments in nature, playing a major role in the color formation and antioxidation in plant flowers and fruits. R2R3-MYB genes are involved in anthocyanin synthesis 81 . In P. mume , 96 R2R3-MYB genes were identified and divided into 35 subfamilies. Finally, the functions of PmMYB1 and PmMYBa1 were identified by overexpression in tobacco and significantly promoted the accumulation of anthocyanins in transgenic tobacco. The flower colors of PmMYB1 -overexpressing transgenic plants were significantly deepened, and the anthocyanin contents in the corolla of transgenic plants were significantly higher than those of the control 82 . To understand the molecular basis of the blue color in water lily, delphinidin 3′-O was identified as the main blue anthocyanidin pigment, and some genes for an anthocyanidin synthase and a delphinidin-modification enzyme were screened by comparing the expression profiles between two N. colorata cultivars with white and blue petals 64 . Interestingly, after the butterfly pea UDP (uridine diphosphate)-glucose: anthocyanin 3′,5′-O-glucosyltransferase gene was introduced in chrysanthemums, blue flowers appeared 83 . In Rosa rugosa , two MYB transcription factors have been confirmed to affect flower color by regulating flavonoid biosynthesis in response to wounding and oxidation 84 . In Paeonia , a chalcone synthase ( PhCHS ) involved in flavonoid biosynthesis and two anthocyanin O-methyltransferase ( AOMT ) genes were consistent with anthocyanin accumulation in petals 85 , 86 .

Candidate genes for controlling floral scent biosynthesis

Floral scent, as one of the quality traits of ornamental plants, has great aesthetic, economic, and application value. The scent components present in petals primarily include secondary metabolites such as esters, alcohols, ketones, aldehydes, terpenes, and volatile phenols, mainly derived from terpene metabolism, phenylpropane metabolism, and the lipoxygenase pathway 87 . There are various types of scent components in different petals, thereby forming distinct scents among various flower species. In a study on the molecular mechanism responsible for the floral scent in P. mume , Zhang et al. 3 first discovered that the benzylalcohol acetyltransferase ( BEAT ) gene can directly catalyze the formation of benzyl acetate, a crucial component of the floral scent in P. mume . Moreover, based on genomic data from P. mume and P. persica , 44 unique PmBEATs were found in P. mume , far more than the 16 in apple, 14 in strawberry, and four in grape. These PmBEAT genes originated from gene duplication events during the species evolution of P. mume , and retroduplication and tandem duplication were the two dominant duplication patterns. Overexpression of the PmBEAT36 or PmBEAT37 genes increased benzyl acetate production in the petal protoplasts of P. mume , and interference in the expression of these genes slightly decreased the benzyl acetate content 88 . Zhao et al. 78 conducted a comparative transcriptome analysis of different developmental stages and tissues of flower genes associated with floral traits and preliminarily selected 12 new genes involved in floral scent formation in P. mume . Furthermore, five of the TFs ( bHLH4 , bHLH6 , bZIP4 , ERF1 , and NAC1 ) from Phalaenopsis bellina have been proven to be involved in orchid floral monoterpenes 89 . In Plumeria rubra , PrCYP79D73 is involved in floral volatile organic compounds and other nitrogen-containing volatiles 90 .

Candidate genes for controlling plant architecture

Rich and diverse plant architectures are the result of long-term evolution, natural selection, and a complex regulatory process of interaction between genetics and the environment. Diverse plant architecture traits are not only conducive to the creation of rich and diverse horticultural landscapes but are also favorable for plant adaptation to complex environments and competition and the utilization of light and nutrients. Along with the completion of whole-genome sequencing for multiple ornamental plants of the genus Prunus , the results lay an important data foundation for studying the molecular genetic mechanisms of pendulous traits 3 , 91 . According to the eight scaffolds of the P. mume genome, Zhang et al. constructed a high-density genetic map using specific-length amplified fragment sequencing (SLAF) and mapped QTLs for major traits such as plant type, flower color, petals, and leaves in P. mume . They found 10 SLAF markers that were closely linked to the pendulous traits of P. mume . Using these markers, the pendulous traits were finely mapped to a 1.14 cM region on chromosome 7, and 36 candidate genes that might be associated with the pendulous traits of P. mume were predicted 92 . Breakthroughs were also achieved in the mining and labeling of genes for weeping and dwarf traits in peach ( P. persica ) by using genome and bulked segregant analyses 93 .

Candidate genes for controlling dormancy release

Flowers of the genus Prunus , such as P. mume and P. yedoensis , are early flowering types in spring. Zhang et al. 3 explored the molecular mechanisms underpinning dormancy break and flowering in P. mume at low temperature. These researchers identified a total of six dormancy-associated MADS-box ( DAM ) genes with a tandem repeat distribution in the genome. The six DAM genes in P. mume are derived from a series of duplication events in the following order: PmDAM1 , PmDAM3 , PmDAM2 , PmDAM5 , PmDAM4 , and PmDAM6 . The molecular evolution pattern of DAM genes is unique to Prunus plants and is present in P. persica , but tandem genes have not been found in M. domestica or F. ananassa . This phenomenon could be related to the earlier flowering of Prunus plants, including P. persica , P. mume , apricot ( Armeniaca vulgaris ) and sweet cherry ( Prunus avium ), than of most other flowering species 3 . DAM genes are regulated by C-repeat-binding transcription factors (CBFs). A conserved CBF site was found 1000 bp upstream of the transcription start site of DAM4 - DAM6 in P. persica and plum ( Prunus salicina ). The latest research results show that a sense-response relationship between PmCBFs and PmDAMs is exhibited in cold-induced dormancy and is jointly regulated by six PmCBFs and PmDAM4–6 94 .

Candidate genes for controlling self-incompatibility

Self-incompatibility has always been an important research topic in the molecular genetic biology of flowers. According to different hereditary patterns of pollen incompatibility phenotypes, the regeneration disorder whereby plants reject self-pollen can be divided into sporophytic self-incompatibility and gametophytic self-incompatibility 95 . Various flowers of the Rosaceae family, including P. mume , P. yedoensis and P. persica , all exhibit gametophytic self-incompatibility, which is controlled by an S-locus with multiple alleles, including two linked genes: one is the S-RNase gene specifically expressed in pistil tissue, and the other is the S-haplotype-specific F-box gene specifically expressed in pollen 96 . In Tarenaya hassleriana , three syntenic regions containing most of the genes of the S-locus were found, and it was assumed that the single-copy ancestral region contained homologs of Pub8 , ARK3 , and B120 23 .

Candidate genes for controlling disease resistance

Disease resistance is an essential trait that attracts research attention across all flowering plants. Thus, the whole-genome analysis also focuses on the genes associated with disease resistance. The genes involved in plant disease resistance are mainly R genes, which encode proteins with extremely high structural similarities, such as leucine zippers, nucleotide-binding sites, transmembrane domains, leucine-rich repeats, and similar extracellular regions of drosophilid toll protein and mammalian toll and interleukin-1 receptor (TIR). Nucleotide-binding site leucine-rich repeat genes constitute the gene family with the widest distribution and largest number of plant R genes. In their encoded proteins, the nucleotide-binding site is present near the N-terminus, while the leucine-rich repeat exists near the C-terminus. The N-terminus of proteins encoded by different genes may also include one or more of the following two conserved structures: the coiled-coil motif and TIR motif. In the P. mume genome, 253 leucine-rich repeats receptor-like kinase (LRR-RLK) genes were identified, and most pathogenesis-related (PR) gene families were notably expanded and arranged in tandem, especially PR10 3 . In Hibiscus syriacus , resistance (R) genes account for 0.53% of its total predicted genes, which is lower than that of other plants evaluated in genomic studies (0.63 to 1.35%) 41 . The Asparagus setaceus genome included 76 R genes with nucleotide-binding sites (NBSs), and the R genes belonged to five groups: TIR-NBS, CC-NBS-LRR, NBS-LRR, NBS, and CC-NBS. NBS-LRR was the largest group, including a total of 29 genes 65 .

Candidate genes for controlling abiotic stress resistance

Adverse conditions such as low temperature, humidity, heat, drought, and saline-alkali conditions severely inhibit the growth and development of ornamental plants. These conditions can cause changes in plant physiology, biochemistry, and morphology and even lead to death. Due to this issue, cultivation facilities for ornamental plants are cumbersome and cannot be widely promoted, which considerably affects their qualities and benefits. Low temperature is an important factor that constrains the normal growth, development, and geographical distribution of plants. Stress caused by low temperature can be divided into chilling stress (>0 °C) and freezing stress (<0 °C). Plants from the tropics and subtropics are more sensitive to cold; in contrast, plants from temperate regions have evolved complex mechanisms to resist and adapt to chilling (freezing) stress, protecting the plants from injury. Cold acclimation is a responsive protection mechanism for plant adaptation and resistance to low-temperature stress, and this process is regulated by a complex network 97 . In particular, the CBF pathway is considered the most important and well-studied pathway 98 . Based on the genome data for P. mume , 30 LEA genes were identified, and heterologous expression of PmLEA increased the cold resistance of Escherichia coli and tobacco ( Nicotiana tabacum ) 99 , 100 . Furthermore, a molecular regulation model of the PmDAM and PmCBF genes in response to dormancy and dormancy release of flower buds induced by low-temperature signals was proposed based on yeast two-hybrid and bimolecular fluorescence complementation experiments 94 .

Prospects for whole-genome sequencing data for ornamental plants

The Earth BioGenome Project (EBP) is a massive project in biology that aims to sequence, catalog, and characterize the genomes of all of Earth’s eukaryotic biodiversity over a period of 10 years. For plants, the core scientific problems are to improve crop yields and other agronomically important traits, biofuel production, gene editing, and conservation of endangered species 101 . The 10,000 Plant Genome Sequencing Project (10KP) initiated by the Beijing Genomics Institute in Shenzhen (BGI-Shenzhen) is a landmark effort to catalog plant genomic variation and represents a major step in understanding the tree of life 102 . A tentative plan of the 100 Flowers Genome Sequencing Project has been put forward by the National Engineering Research Center for Floriculture in China. Many ornamentals are marked by high ploidy levels and homologous polyploids (chrysanthemum and alfalfa) or extremely large genome sizes (lily and tulip), which limit the development and utilization of genome sequencing technology in ornamental plants. Along with the development of sequencing and bioinformatics analysis technologies and the continuous emergence of various new biological technologies, genomics research on ornamental plants has developed faster and better. Although genome sequencing and assembly of flowering plants face substantial difficulties, the quality of genome assembly results is relatively high in terms of the analytical results from 69 flower species that underwent genome sequencing, and four of them have been resequenced using updated sequencing technology 5 , 11 , 37 , 50 . As far as we know, there are at least a dozen ornamental plants undergoing the process of genome quality improvement. As more ornamental plant genomes are sequenced, further bioinformatics analysis could reveal crucial basic information on the origin of species and the genes that control flower traits. The development of genomics will surely address the knowledge gaps of traditional breeding methods. The ultimate goal is to obtain the optimal type of flower variety with fixed-point improvement and the aggregation of multiple elite traits by using the most effective and rapid method.

China has 30,000 species of higher (flowering) plants, and some ornamental flowering plants reached Europe quite early 103 . Chinese people love flowers and cultivate many kinds of brilliant flowers, such as mei, peony, chrysanthemum, rose, lily, lotus, and orchid. Due to the rapid development of genome sequencing technology worldwide, large quantities of whole-genome sequencing data are in urgent need of deep mining. A long-term strategic genomics research plan should be formulated that is not limited to cultivated species but considers thorough development of the sequencing of important wild relatives of ornamental species in China and promoting the mining, protection, and utilization of important genetic resources. It is essential to put an end to the dependence on the apparent phenotype, transform investigations into genotype-dependent research and shift from single-gene studies to GWAS. Efforts should be made to vigorously promote the application of genomics in gene cloning and molecular breeding in China and to improve the breeding capacity and level of horticultural crops.

Due to their complexity and particularity, plant genomes have always been an important focus of genomics. Before the second generation of high-throughput sequencing, sequencing costs were high, and the throughput was low. For species with highly repetitive sequences, it was too difficult or too expensive for researchers to obtain the whole-genome sequences of high repeat sequence species. Many species with important economic and ornamental value have not yet been submitted to complete genome sequencing. In short, due to the particularity and diversity of ornamental plants, there are challenges and opportunities in genome research of these species. Challenge: (1) Complex genome. The term complex genome refers to a kind of genome that cannot be directly analyzed by conventional sequencing and assembly methods. It usually refers to a genome containing a high proportion of repetitive sequences, high heterozygosity, extreme GC content, and difficulty in eliminating foreign DNA contamination. (2) Autopolyploidy. Autopolyploidy is common in ornamental plants. It is usually formed by doubling two or more sets of genomes, which is of great value in genetic breeding and agricultural production. Using conventional methods, it is easy to connect incorrect allele fragments together, resulting in the wrong connection of homologous chromosomes and a large number of chimeric assemblies; thus, assembly is still difficult. (3) Megagenome. Megagenome generally refers to species with genomes larger than 10 Gb. The sequencing and analysis of these species are very involved, especially for assembly analysis, which is a major challenge. Paris japonica is an unusual plant. Scientists have found that it has the world’s largest genome, with 150 Gb, which is 50 times more than that of humans. Although the genomes of some ornamental plants have been deemed complete, the assembly quality of some species is poor, and a small number of “holes” have not yet been completed due to technical limitations, although the interest of scientists in this regard is debatable. The latest research shows that the sequences that were once considered irrelevant, or “garbage”, in the genome have their own significance. These missing sequences play a very important role, and we now have the opportunity to mine them. Third-generation sequencing technology (PacBio and Nanopore) can make up for the holes in some genomic regions that are difficult to assemble due to sequencing errors, repeat regions, heterochromatin, genomic polymorphisms, and second-generation sequencing preferences. To solve the challenge of sequencing the genomes of ornamental plants, the following new technologies can be tried with third-generation sequencing technology. (1) Pangenome. The pangenome includes the core genome and the nonessential genome. Among them, the core genome refers to the genes that exist in all individuals; the nonessential genome refers to the genes that exist only in some individuals. (2) Hi-C. The advantages of Hi-C sequencing technology are as follows: on the one hand, there is no need to construct a large number of F 1 populations, as only individuals are needed; on the other hand, the haplotype genome can be separated without parent purification, so this method is suitable for the assembly of a highly heterozygous genome that is not easy to purify.

With the development of sequencing technology, the concepts of difficult genome sequencing and assembly quality have also developed and changed. We cannot sequence everything for the sake of genome sequencing. The purpose of sequencing must be to reveal the key scientific problems of species. We should strengthen research related to transcriptomics, metabolomics, proteomics, degradomics, and phenomics. With more genomic data published, it has become a great challenge to analyze, store and share the massive amounts of genome sequencing data. A key problem is how to solve the time and cost problems faced by researchers to achieve the purpose of reducing repetitive research, improving the practicability of scientific research, mining research content, and improving the transparency of scientific research and data sharing with cross-research into other fields. Moreover, it is necessary to enhance bioinformatics education and apply bioinformatics in practice. With the continuous development of sequencing technology, we believe that the whole-genome sequencing of horticultural crops will enter a rapid development stage in the near future, leading to tremendous contributions to the world’s horticultural industry.

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Acknowledgements

The research was supported by the National Natural Science Foundation of China (No. 31800595 and 31471906), the National Key Research and Development Program of China (2018YFD1000401), and the Special Fund for Beijing Common Construction Project.

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Tangchun Zheng, Ping Li, Lulu Li & Qixiang Zhang

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T.Z. conceived and drafted the manuscript. T.Z., P.L., and L.L. analyzed the data. Q.Z. contributed to the conception of the study and finalized the manuscript. All authors read and approved the final manuscript.

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Zheng, T., Li, P., Li, L. et al. Research advances in and prospects of ornamental plant genomics. Hortic Res 8 , 65 (2021). https://doi.org/10.1038/s41438-021-00499-x

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Effects of Indoor Plants on Human Functions: A Systematic Review with Meta-Analyses

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The influences of indoor plants on people have been examined by only three systematic reviews and no meta-analyses. The objective of this study was therefore to investigate the effects of indoor plants on individuals’ physiological, cognitive, health-related, and behavioral functions by conducting a systematic review with meta-analyses to fill the research gap. The eligibility criteria of this study were (1) any type of participants, (2) any type of indoor plants, (3) comparators without any plants or with other elements, (4) any type of objective human function outcomes, (5) any type of study design, and (6) publications in either English or Chinese. Records were extracted from the Web of Science (1990–), Scopus (1970–), WANFANG DATA (1980–), and Taiwan Periodical Literature (1970–). Therefore, at least two databases were searched in English and in Chinese—two of the most common languages in the world. The last search date of all four databases was on 18 February 2021. We used a quality appraisal system to evaluate the included records. A total of 42 records was included for the systematic review, which concluded that indoor plants affect participants’ functions positively, particularly those of relaxed physiology and enhanced cognition. Separate meta-analyses were then conducted for the effects of the absence or presence of indoor plants on human functions. The meta-analyses comprised only 16 records. The evidence synthesis showed that indoor plants can significantly benefit participants’ diastolic blood pressure (−2.526, 95% CI −4.142, −0.909) and academic achievement (0.534, 95% CI 0.167, 0.901), whereas indoor plants also affected participants’ electroencephalography (EEG) α and β waves, attention, and response time, though not significantly. The major limitations of this study were that we did not include the grey literature and used only two or three records for the meta-analysis of each function. In brief, to achieve the healthy city for people’s health and effective functioning, not only are green spaces needed in cities, but also plants are needed in buildings.

1. Introduction

Throughout history, humans have valued the health benefits of contact with nature [ 1 ]. Theoretically, an evolutionary perspective suggests that evolutionary processes enable humans to respond adaptively and positively to nature [ 2 ], whereas a cultural perspective contends that culture affects people’s relations with the natural environment [ 3 ]. In line with the evolutionary perspective, the concept of biophilia claims that humans are born with emotional connections with nature and/or other living organisms [ 4 ]. This emotional predisposition is deeply embedded in the biological nature of humans and does not disappear even after people leave the natural environment to live a modern urban life [ 5 ]. Moreover, the Stress Reduction Theory (SRT; [ 3 ]) emphasizes that stress is “the process by which an individual responds psychologically, physiologically, and often with behaviors, to a situation that challenges or threatens well-being” ([ 6 ], p. 202), and the natural environment is helpful for recovery from stress, whereas the Attention Restoration Theory (ART; [ 7 ]) emphasizes that the natural environment is beneficial to the restoration of directed attention for people’s effective functioning. Empirically, an increasing number of studies on human interaction with nature have demonstrated that contact with nature is favorable to human emotions, physiological functioning, attention restoration, behavior, and health [ 8 , 9 , 10 ]. Scholars have also conducted systematic reviews (e.g., [ 11 , 12 , 13 , 14 , 15 ] and meta-analyses on related topics (e.g., [ 16 , 17 , 18 , 19 , 20 , 21 ]). In total, by 2022, more than 60 reviews and meta-analyses regarding nature and health and well-being had been conducted (cf. [ 22 ]).

Despite long interests in the theoretical and empirical value of nature to humans, at present, 55% of the world population lives in cities, and the urban population worldwide is expected to increase by 68% by 2050 [ 23 ]. For this reason, the World Health Organization Regional Office for Europe in 2016 [ 24 ] published a report titled “Urban Green Spaces and Health—A Review of Evidence” to address the importance of nature and green spaces for urban living. The World Health Organization also advocates the healthy city, defined as “one that continually creates and improves its physical and social environments and expands the community resources that enable people to mutually support each other in performing all the functions of life and developing to their maximum potential” [ 25 ]. Individuals in contemporary society nevertheless spend most of their time indoors [ 26 ], with urban dwellers spending more than 80% of their life indoors [ 27 , 28 , 29 ]. Moreover, urbanities often do not have ready access to nature [ 30 ]. Consequently, urbanites have few opportunities to maintain contact with nature. Although nature includes many elements, plants are the most representative symbol of nature [ 31 , 32 ]. Similarly, “green space” refers to open, underdeveloped, naturally planted land [ 33 ], land with grass or trees, or other vegetation region [ 34 ]. Studies of indoor nature also tend to focus on plants [ 35 , 36 ]. The exploration of the physical and psychological benefits of indoor plants on people, therefore, merits more attention [ 37 , 38 ]. Interior environments and indoor plants could be important elements of the healthy city. The Rural Development Administration of South Korea suggests placing one small potted plant and one large potted plant per 6 m 2 floor area in a room to improve the indoor quality [ 39 ]. Systematic reviews and/or meta-analyses of the effects of indoor plants on people, however, are far less common than those on natural environments and/or green spaces.

There are only three narrative reviews on the influences of indoor plants related to people. Bringslimark et al. [ 31 ] reviewed 21 articles of the experimental research focusing on the benefits of indoor plants on people, which identified benefits such as stress reduction and pain tolerance enhancement. This study was a great stepping stone for later research, particularly with respect to experimental design, measurement, analysis, and reporting. Given that this narrative review was published more than a decade ago, updates are necessary, as is a further distinction of the benefits identified as either self-reported perceptions or objectively measured outcomes using devices or tasks. Deng and Deng [ 40 ] reviewed the importance of indoor plants to human health with respect to photosynthesis, transpiration, psychological effects, and air purification, indicating the influence of indoor plants on task performance, health, and stress. Moya et al. [ 41 ] reviewed 104 articles published in specific journals between 1984 and 2017 on the influence of vegetation on indoor environmental quality, finding that indoor plants improved people’s comfort, satisfaction, and happiness but presented no strong evidence of improvements in performance and productivity. The inconsistent findings on the influences of indoor plants on participant’s performance [ 40 , 41 ] await further clarification. Further, these three narrative reviews did not follow the rigorous Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA; [ 42 ]), which may have resulted in subjectivity and a lack of transparency and comprehensiveness [ 43 ]. They also did not cover studies published in widely used languages, such as Chinese.

Recently, three systematic reviews were conducted to address the gaps left by previous narrative reviews of research on indoor plants and human responses. One followed the Centre for Reviews and Dissemination (CRD) guidelines [ 44 ], and two followed the PRISMA guidelines. The first systematic review [ 45 ] following the PRISMA covered studies published in English and Chinese—two of the most common languages in the world—focused on self-reported perceptions and included 50 empirical studies, which concluded that the primary beneficial effects of indoor plants were an increase in positive emotions and a reduction in negative feelings, while secondary benefits included a reduction in physical discomfort. The second systematic review [ 36 ] following the CRD covered 26 studies of the health and well-being impacts of indoor nature (actual and simulated plants and aquariums) on the elderly and concluded that higher-quality studies showed that indoor gardening programs were helpful for cognition, psychological well-being, social outcomes, and life satisfaction. The third review [ 35 ] following the PRISMA covered 37 studies published in English and Dutch on the influences of indoor and outdoor nature on adolescents, which found associations between outdoor campus green space and enhanced quality of life and perceived restoration. The common findings of the two systematic reviews are that indoor plants benefit psychological well-being [ 36 , 45 ]. Self-reported psychological responses, however, may be different from actual human functions (cf. [ 46 ]). Moreover, Yeo et al. [ 36 ] researched only older adults and did not specifically focus on indoor plants. Van den Bogerd et al. [ 35 ] researched only adolescents and did not specifically focus on indoor plants. Furthermore, none of these three reviews conducted meta-analyses to provide quantitatively synthesized evidence of the effects of indoor plants on humans. This may be because of the heterogeneity of the outcomes.

Given the above-mentioned factors, the purpose of the present study was to perform a systematic review with meta-analyses of Chinese and English empirical quantitative research on the influences of indoor plants on human functions, in order to address the current research gap of the lack of meta-analyses on this subject and to respond to the fulfillment of the daily functions of urbanites as advocated by the promotion of the healthy city. Specifically, the objective of this study was to examine if the presence of indoor plants of any type serving as an intervention has any objectively measured effects, such as using devices, tasks, examinations, or performance records, on human functions. We reviewed all research with any study design that assessed all human functions exposed to indoor plants against those exposed to no indoor plants or other elements. Accordingly, the review question was whether indoor plants have any effects on human functions. The present systematic review may provide more comprehensive information associated with the aforementioned effects and serve as a reference for future research. This study identifies what empirical and quantitative studies of human functions have been performed in relation to indoor plants, particularly regarding research validity (cf. [ 31 ]), such as plant quantity measurements (construct validity: number, size, volume percentage, and green coverage ratio), potential effect modifiers (confounder: exposure duration, distance to plants, room climate, and room size), funding (conflict of interest), and what and how further research could be performed. The meta-analyses further examined the overall results of studies exploring the effects of indoor plants on human functions, rather than reviewing studies individually. Systemic reviews and meta-analyses are effective in providing optimal synthesis evidence, and the constantly updated data may serve as a basis for policy making [ 43 ], such as regarding the healthy city or effective human functions [ 25 ]. The systematic review and meta-analyses conducted in this study are the first to provide a synthesis of the quantitative evidence regarding the specific effects of indoor plants on human functions.

This study followed the PRISMA guidelines, particularly their specific checklist items and item orders, although PRISMA focuses on evaluating interventions in the field of medical care [ 42 ]. The conduct of the review involved no significant deviations from the protocol, except that we searched two more databases than the protocol.

2.1. Eligibility Criteria

The eligibility criteria for inclusion of a study in this research were as follows: (1) participants of any type were recruited; (2) no criteria were set for the type of indoor plant to be used in interventions; (3) the comparator was participants in an indoor environment without any plants or with other elements; (4) the outcome included any type of objectively measured human function, such as use of devices, performance tasks, examinations, or records, rather than self-reports; (5) all types of study design were included; and (6) the language was either English or Chinese. Because Chinese and English are the most commonly used languages in the world, studies written in these two languages were selected to decrease the risk of language bias [ 43 ]. Other languages were not included because of limited resources.

2.2. Information Sources

The information sources included four electronic databases, of which the Core Collections hosted by Web of Science (1988–) and Scopus (1970–) are English-language databases, while the Journal Collections hosted by WANFANG DATA (1980–) and Taiwan Periodical Literature (1970–) are Chinese-language databases. At least two databases, therefore, were searched for each of the two languages. The final search on WANFANG DATA was performed on 14 August 2019, while that on the Web of Science was performed on 11 November 2019. The search on Taiwan Periodical Literature was performed on 21 October 2020, and the search on Scopus was performed on 13 November 2020. We searched WANFANG DATA and Web of Science in the first round and Taiwan Periodical Literature and Scopus in the second. About one year thus elapsed between the searches of the two rounds. The follow-up searches of all four databases were completed on 18 February 2021. The coverage cutoff date was 31 December 2020. We decided that the coverage ended at the end of 2020 rather than in the middle of the year, so later updated searches could continue at the start of 2021. Moreover, two supplementary approaches to identifying studies were applied: one was that the related studies were identified by reference searches of the included studies, while The other was contact with the authors of the included studies to seek missing information, particularly regarding the results.

2.3. Search

The search terms included the following: “indoor”, “interior”, “architecture”, “building”, “plant”, “vegetation”, “greening”, “greenery”, “green”, “greenness”, “perception”, “psychology”, “emotion”, “physiology”, “cognition”, “restoration”, “behavior”, “health”, and “performance”, as found in previous studies [ 8 , 45 , 47 ] and in peer reviewers’ suggestions. In the Boolean search, only “AND” was adopted as the operator, as in (1) indoor “AND” plant “AND” perception, or (2) architecture “AND” greening “AND” psychology. Except for the eligibility criteria and the search coverage, we did not have any restrictions such as topics, keywords, or dates. The full search strings applicable to all four databases are listed in Supplementary Material Table S1 .

2.4. Study Selection

The present systematic review included only quantitative empirical studies published in journals, primarily because of their relatively easy accessibility. Technical reports, proceedings, books, and unpublished theses or dissertations (i.e., grey literature) therefore were not considered. Empirical studies using plants in a room or building as the intervention, irrespective of how many plants, what sizes, what types, foliage or floral, actual or virtual, duration of presence, or distance from the participants, were included in accordance with the eligibility criteria. “Empirical research” refers to the analysis of real data, and quantitative research uses computation, mathematics, and statistics to explore the target phenomenon [ 48 ]. Regarding the causal relationship between variables in quantitative research, randomized controlled experiments, in which participants are randomly assigned to experimental and control groups (also referred to as “RCT” in clinical professions), provide higher-quality results than nonrandomized controlled quasi-experiments, in which participants are not randomly assigned to experimental and control groups (also referred to as “non-RCT”), and quasi-experiments outperform surveys [ 49 ]. Field experiments conducted in real-world environments, however, exhibit more favorable ecological validity than laboratory experiments [ 50 ]. If surveys were used to collect objective outcomes such as health indicators, they were also included.

2.5. Data Collection Process

L.-W.R. performed searches with the abovementioned terms in the databases and reviewed study titles and abstracts that met the eligibility criteria. L.-S.L. independently performed searches with the same terms in the same databases and reviewed study titles and abstracts that met the eligibility criteria. As a result, L.-W.R. and L.-S.L. had an agreement rate of 99.9% on both Web of Science and WANFANG DATA, respectively, and L.-S.L. and K.-T.H. also had an agreement rate of 99.9% on Taiwan Periodical Literature. In cases where the title and abstract were insufficient to determine the study’s eligibility, L.-W.R. or L.-S.L. proceeded to read the full text. All the studies of each included paper were reviewed. Then, K.-T.H. reviewed the extracted full-text studies that met the eligibility criteria. K.-T.H. and L.-W.R. conducted data extraction and quality appraisal. Initial disagreement regarding a study’s opinion was resolved by discussion between the two reviewers.

2.6. Data Items

The following 14 data items were extracted from the reviewed records: sources, participants, interventions, comparator, exposure duration, distance to plants, room climate, room size, study design, functions, function categories, outcomes, funding, and languages.

2.7. Risk of Bias in Individual Studies

The included studies were analyzed in accordance with the quality appraisal system proposed by Ohly et al. [ 19 ]. This appraisal system comprises 19 appraisal items, including quality indicators from the CRD [ 44 ], critical appraisal checklists from the Critical Appraisal Skills Program [ 51 ], and quality assessment tool for quantitative studies from the Effective Public Health Practice Project [ 52 ]. We adopted the quality appraisal system because it was more comprehensive and current than other appraisal systems. This appraisal system, which has an option of criterion inapplicable to this study design, was applied to both RCTs and nonrandomized studies [ 19 , 20 ].

2.8. Summary Measures

The summary measures of this study included data measured in empirical research using devices, tasks, academic achievement scoring, and actual health indicators. These data were reviewed to examine the influences of indoor plants on participants’ functions.

2.9. Planned Methods of Analysis

Where sufficient studies (at least two studies) using comparable outcome measures allowed us to conduct meta-analyses, the present meta-analyses reported the means and standard deviations (SDs) of each function category. Comprehensive Meta-Analysis version 3 (Biostat, Englewood, NJ, USA) was applied to conduct Cochran’s Q tests and draw forest plots as well as to analyze pooled effect sizes, sensitivities, and publication biases. Because the measurement of functions in similar categories varied between the records, the measurement outcomes of these categories were processed using the standardized mean difference (SMD), thereby providing an indicator enabling the comparison and synthesis of function outcomes in these categories (cf. [ 43 ]). For records using the same methods to measure function in the same categories, outcomes were, in general, directly compared and synthesized to determine the mean differences (MDs). For studies with more than one experimental group [ 53 ], each experimental group and control group was separately analyzed [ 43 ]. Specifically, Cochran’s Q test was performed to examine whether the classification outcomes of function in each category were heterogeneous or homogenous. Additionally, forest plots were adopted to present the relative importance and research outcome directions among the studies visually. Subsequently, the pooled effect size was computed using fixed-effect or random-effect models.

2.10. Risk of Bias across Studies

The meta-analyses used funnel plots and Egger’s regressions to identify potential publication bias on the basis of the research results of each function category.

2.11. Additional Analyses

The meta-analyses included the sensitivity analysis of the results of the records for each function category, which examined if the pooled effect sizes changed notably when any of the records was removed—an indication of the stability of the results.

3.1. Study Selection

The abovementioned terms were used to search the four databases separately. The search yielded 30,887 records from the Web of Science, 4323 from WANFANG DATA, 30,203 from Scopus, and 4105 from Taiwan Periodical Literature. Repeated records were excluded. Moreover, 11 records were identified after searching the references of the searched papers (which were considered as other sources), resulting in 31,728 journal articles in total. Papers with titles and abstracts meeting the eligibility criteria were identified, resulting in 63 preliminarily qualified papers. The full texts of these 63 papers were extracted for further scrutiny, and 21 studies that failed to meet the criteria were excluded. As a result, 42 qualifying records were included ( Figure 1 ). The major reasons for excluding records were that the research was not empirical and quantitative, human functions were not objectively measured, and plant functions were measured ( Supplementary Material Table S2 ).

Flow chart of the screening process.

3.2. Study Characteristics

Among the 42 journal articles included in the systematic review, 5 (11.9%) and 37 (88.1%) were written in Chinese and English, respectively. The earliest paper was published in 1996, and the latest in 2020 (the terminus of the search coverage). The 25 year coverage period was divided into 5 year intervals to analyze the number of publications during each interval. The number of published papers increased relatively steadily ( Table 1 ).

Statistics of published journal articles in Chinese and English during consecutive 5 year periods.

In terms of geographical distribution, most of the studies were from China (10; 23.8%), followed by the United States (8; 19.0%), Japan (6; 14.3%), South Korea (5; 11.9%), and Taiwan (4; 9.5%). Asia was thus the leading continent, followed by America, Europe, and Africa. Most studies were from the Global North, followed by the Global South and the Equatorial region ( Table 2 ). Detailed statistics could not be compiled because not every record provided the participants’ socioeconomic backgrounds. The majority of the participants, however, were college students. Only six studies recruited office workers [ 54 , 55 , 56 , 57 , 58 , 59 ], five studies recruited patients [ 60 , 61 , 62 , 63 , 64 ], two studies recruited junior high school students [ 65 , 66 ], and one study recruited high school students as participants [ 67 ] ( Table 2 ).

Statistics of geographical distribution of the included studies.

The records generally did not focus on only one measure of human functions. The reviewers found that they examined 52 functions. Most of the records were related to physiology (27; 51.9%), followed by cognition (15; 28.8%), health, (seven; 13.5%), and behavior (three; 5.8%). Concerning study design, most of the records adopted experimental methods (26; 61.9%). These were followed by those conducting field experiments (seven; 16.7%), field quasi-experiments (five; 11.9%), and surveys (four; 9.5%). Among the 42 records, 20 reported the specific number of indoor potted plants as the intervention; the highest number of potted plants was 34 [ 66 ], and the lowest number of potted plants was one [ 56 , 59 , 60 , 68 , 69 , 70 , 71 ]. Three papers reported the green coverage ratio, with the highest at 10% and the lowest at 3% [ 57 ]. Two papers also indicated the volume of indoor plants as a percentage of the total experimental space, where the largest volume was 17.9% [ 53 ] and the smallest was 5% [ 67 ] ( Table 3 ). In addition, three records used photographs or slides as surrogates for indoor plants [ 72 , 73 , 74 ], and one paper employed virtual-reality plants [ 75 ] ( Table 4 ).

Summary of the study characteristics of the records.

RH: relative humidity; SBP: systolic blood pressure; DBP: diastolic blood pressure; EEG: electroencephalography; EDA: electrodermal activity; EMG: electromyography; BVP: blood volume pulse; ECG: electrocardiography; GSR: galvanic skin response; RCT: randomized controlled trial; non-RCT: not randomized controlled trial.

Statistics of experimental conditions.

A total of 34 papers recorded the time during which participants were exposed to indoor plants. Among these, the longest exposure time was one year [ 76 ] and the shortest was 15 s [ 72 ]. Thirty-three papers reported the room size. The experiment room used by Toyoda et al. [ 59 ] was the largest in terms of its floor area (1260 m 2 ), and that used by Genjo et al. [ 57 ] was the largest in terms of its volume (675 m 3 ). By contrast, the room used by Kim et al. [ 77 ] was the smallest in both floor area (7.26 m 2 ) and volume (14.52 m 3 ). Among the records, only 13 reported the participant–plant distance in a room, with the greatest distance being 3 m [ 72 ] and the smallest being 0.38 m [ 60 ] ( Table 3 ).

Some records also provided data on the ambient environment in which the plants were placed. Specifically, 19 papers recorded the room temperature, with the highest being 27 °C [ 78 ] and the lowest 20 °C [ 59 ]. Humidity was reported in 13 papers, with the highest value at 70% [ 79 ] and the lowest 34% [ 80 ]. Only one record measured wind speed (0.2 m·s −1 ; [ 81 ]). Twelve records indicated lighting, of which only one adopted the quantum as the lighting unit (10.6 μmol m −2 ·s −1 ; [ 69 ]), whereas the remaining 11 used illuminance as the unit. The most intense lighting was 1365.5 lux [ 82 ], while the least intense lighting was 300 lux [ 56 ] ( Table 3 ).

Among the 42 records, only 18 indicated their funding sources. Most of the funding sources were in governmental sectors, while only two may be from stakeholders ([ 83 ], American Horticultural Therapy Association; [ 68 ], The Swedish Flower Corporations) ( Table 4 ). Funding from stakeholders might cause a conflict of interest.

3.3. Risk of Bias within Studies

Most of the included studies (90.5%) applied quasi-experimental or experimental methods. Control and experimental groups were therefore involved. In quasi-experimental research, particularly field research (11.9%), researchers were unable to assign interventions randomly to participants as is the case in clinical trials. Surveys, field quasi-experiments, and quasi-experiments, therefore, could not achieve sequence generation, which reduces the risk of bias. In addition, concealing the intervention assignment from participants was difficult because indoor plants were easily noticed in a room, resulting in lower allocation concealment ability. Similarly, blinding participants concerning their intervention was also challenging. Furthermore, the risk of incomplete data on outcomes caused by participant attrition and exclusion might exist because the included studies seldom mentioned participant attrition or exclusion.

The mean quality appraisal score of the 42 records was 17.2 points out of a possible 38, i.e., 45.3% (17.2/38 = 45.3%) of the total, indicating moderate research quality (high: 67–100%, moderate: 34–66%, low: 0–33%; [ 19 ]). The five items (of a total of 19) in the quality appraisal system for which the records included scored lowest are discussed next. First, none of the 42 papers complied with the intention-to-treat (ITT) analysis (0%) (i.e., all data were included after allocation). Additionally, the participants were not sufficiently representative because most were students (17 studies included college students, 1 study included high school students, and 2 studies included junior high school students). Only 5 papers involved general adult participants, whereas the remaining papers involved patients or office workers. The second lowest score regarding the quality appraisal system was found in the only 1 paper (2%) in which the outcome assessors were completely unaware of participant allocation. The third lowest scores were observed in the following two items of the quality appraisal system: only 2 papers (5%) reported statistical power and randomization procedure, respectively ( Table 5 and Table 6 respectively). The records exhibited desirable quality in the following items of the appraisal system: (1) all the papers (100%) included individual level analyses, (2) data collection in 39 studies (95%) was consistent, (3) a total of 37 studies (90%) provided a clear description of interventions and control, and (4) 32 papers (78%) accounted for all participants and applied statistical analysis methods appropriate for study design.

Quality appraisal of records in this study.

ITT: intention to treatment; Yes = 2; Partial (Pa.) = 1; No = 0; Unclear (Un) = 0; NA = criterion inapplicable to this study design; any changes made after consultation with study authors are highlighted in boldface. Appraisal quality: High (H): 67–100%, Moderate (M): 34–66%, Low (L): 0–33% [ 19 ].

Statistics of quality appraisal of records in this study.

3.4. Results of Individual Studies

The research outcomes of each study for the systematic review are summarized in Table 7 . In brief, the systematic review concluded that indoor plants, in general, affect participants’ functions positively, particularly their physiology and cognition. Regarding physiological functions, participants exhibited greater benefits in a room with plants than in a room without plants in relation to lower blood pressure [ 60 , 61 , 63 , 76 , 78 , 82 ], lower electrodermal activity (EDA) [ 69 , 83 , 85 ], lower electroencephalography (EEG) α and β waves [ 56 , 69 , 72 , 81 , 83 ], lower heart rate [ 59 , 61 , 62 , 63 , 68 , 76 , 91 , 93 ], and lower respiration rate and body temperature [ 61 ].

Summary of the outcomes of the records.

SBP: systolic blood pressure; DBP: diastolic blood pressure; EEG: electroencephalography; EDA: electrodermal activity.

Regarding cognitive functions, when indoor plants were present, participants exhibited higher academic achievement [ 66 , 86 ] and better performance in various cognitive tasks [ 58 , 71 , 75 , 77 , 78 , 84 , 87 , 94 ]. In health-related functions, with exposure to indoor plants, participants less frequently took sick leave [ 54 , 55 , 65 , 67 ], consumed fewer pain killers [ 61 , 63 , 64 ], and had fewer hospitalization days [ 64 ] than participants in environments where indoor plants were absent. In behavioral functions, participants presented greater pain tolerance of putting hands in cold water [ 80 , 85 ] and less misconduct [ 65 ] when indoor plants were in the room than when indoor plants were not in the room.

3.5. Synthesis of Results

The data for the meta-analyses included only the participants’ physiological functions (i.e., diastolic blood pressure (DBP), EEG α and β waves) and cognitive functions (i.e., attention, academic achievement, and response time) because at least two studies are needed to conduct the meta-analyses. Given that the number of the records of each of the function categories was small, randomized control trials and non-randomized studies of interventions were included for the meta-analyses. Moreover, various interventions of indoor plants regardless of species, type, quantity, exposure time, and distance to participants were dichotomized as groups with plants and groups without plants.

Three papers examining the influence of indoor plants on DBP, which was measured by sphygmomanometers measured in mmHg, were included for the meta-analysis ( Table 8 ). In total, 248 participants were evenly exposed to conditions either with plants or without plants. Lee et al. [ 82 ] recruited only male adults in South Korea, whereas Hassan et al. [ 60 ] recruited only female older adults with high blood pressure in China. Chen et al. [ 76 ] surveyed male and female elders in Taiwan six times over one year. Both Lee et al. [ 82 ] and Hassan et al. [ 60 ] randomly assigned their participants to different groups, while Chen et al. [ 76 ] did not. All three papers were appraised as having moderate research quality.

Original data of the studies examining the influence of indoor plants on DBP.

The heterogeneity test of the three studies focusing on DBP revealed a significant difference ( p < 0.05) with I 2 = 97.554%, confirming high heterogeneity among the studies. A random-effect model was therefore applied. Given that the standard deviation (SD) of one study was much smaller than that of the other two, SMD, rather than MD, was adopted here. The pooled effect size (SMD) was −2.526 with a 95% confidence interval ranging between −4.142 and −0.909. The results indicated that the group with plants had significantly ( p = 0.002) lower DBP values than the group without plants ( Table 9 ). The relative weight of both the Hassan et al. [ 60 ] and Chen et al. [ 76 ] studies was about 37.00%, and that of Lee et al. [ 82 ] was 25.29% ( Figure 2 ).

Forest plot of studies on the influence of indoor plants on DBP [ 60 , 76 , 82 ].

Heterogeneity test results of studies on the influence of indoor plants on DBP.

3.7. EEG α Waves

Three papers examining the influence of indoor plants on EEG α waves, which was measured by brain activity instruments with Hertz as the unit of measurement, were included for the meta-analysis ( Table 10 ). The studies had a total of 200 participants. Among them, 85 were in the control group (without plants) and 115 in the experimental group (with plants). Chang and Chen [ 72 ] recruited college students in Taiwan and Qin et al. [ 81 ] recruited college students in China, whereas Elasdek and Liu [ 56 ] recruited only female office workers in China. Chang and Chen [ 72 ] and Elasdek and Liu [ 56 ] did not randomly assign their participants to different groups, while Qin et al. [ 81 ] did. These three papers were appraised as having moderate research quality.

Original data of the studies examining the influence of indoor plants on EEG α waves.

The heterogeneity test of the three studies investigating the influence of indoor plants on EEG α waves revealed a significant difference ( p < 0.05), with I 2 = 94.488%, confirming high heterogeneity among the studies. A random-effect model was therefore adopted. The pooled effect size (MD) was 1.140, and the 95% confidence interval ranged from −0.260 to 2.540. The results indicated that the group with plants had greater EEG α waves than the group without plants, but the difference was nonsignificant ( p = 0.110) ( Table 11 ). The relative weight of both the Chang and Chen [ 72 ] and Elasdek and Liu [ 56 ] studies was about 34.6%, and that of Qin et al. [ 81 ] was 30.72% ( Figure 3 ).

Forest plot of studies on the influence of indoor plants on EEG α waves [ 56 , 72 , 81 ].

Heterogeneity test results of studies on the influence of indoor plants on EEG α waves.

3.8. EEG β Waves

Only two papers examining the influence of indoor plants on EEG β waves, which was measured in Hertz by brain activity instruments, were included in this meta-analysis ( Table 12 ). In total, 110 participants were evenly assigned to groups either with plants or without plants. Chang and Chen [ 72 ] recruited college students in Taiwan and Qin et al. [ 81 ] recruited college students in China. Chang and Chen [ 72 ] did not randomly assign their participants to different groups, while Qin et al. [ 81 ] did. Both papers were appraised as having moderate research quality.

Original data of the studies examining the influence of indoor plants on EEG β waves.

The heterogeneity test of the two studies investigating the influence of indoor plants on EEG β waves revealed a significant difference ( p < 0.05), with I 2 = 97.133%, confirming high heterogeneity between the studies. A random-effect model was therefore adopted. The pooled effect size (MD) was 1.455, and the 95% confidence interval ranged from −1.799 to 4.709. Though the results indicated that the group with plants had greater EEG β waves than the group without plants, the difference was not significant ( p = 0.381) ( Table 13 ). The relative weight of both the Chang and Chen [ 72 ] and Qin et al. [ 81 ] studies was about equal, at 50.95% and 49.05%, respectively ( Figure 4 ).

Forest plot of studies on the influence of indoor plants on EEG β waves [ 72 , 81 ].

Heterogeneity test results of studies on the influence of indoor plants on EEG β waves.

3.9. Attention

Three papers examining the influence of indoor plants on attention, which was measured by various cognitive tasks with the unit of measurement as performance scores, were included for the meta-analysis ( Table 14 ). In total, 177 participants were randomly assigned to different groups. Because Larsen et al. [ 53 ] divided the participants into two experimental groups (with a high or moderate number of plants) and one control group (without plants), there were 76 participants and 101 participants in the control and experimental groups, respectively. Larsen et al. [ 53 ] recruited participants in the United States, Yin et al. [ 75 ] recruited adults in the United States, and Shibata and Suzuki [ 71 ] recruited college students in Japan. All three papers were appraised as having moderate research quality.

Original data of the studies examining the influence of indoor plants on attention.

The heterogeneity test of the three studies (one with two experimental groups) investigating the influence of indoor plants on attention revealed a significant difference ( p < 0.05), with I 2 = 82.088%, confirming high heterogeneity among the studies. A random-effect model was therefore adopted. The pooled effect size (SMD) was −0.005, and the 95% confidence interval ranged from −0.671 to 0.661. The results indicated that the group with plants had lower attention than the group without plants. The difference, however, was not significant ( p = 0.988) ( Table 15 ). The relative weight of the three studies was relatively similar, ranging from 25.85% to 23.32% ( Figure 5 ).

Forest plot of studies on the influence of indoor plants on attention [ 53 , 71 , 75 ].

Heterogeneity test results of studies on the influence of indoor plants on attention.

3.10. Academic Achievement

Only two papers examining the influence of indoor plants on academic achievement, which was measured by course grades and examination scores, were included for the meta-analysis ( Table 16 ). The studies had a total of 119 participants. Among these, 58 were in the control group (without plants) and 61 in the experimental group (with plants). Doxey et al. [ 86 ] recruited sophomores in the United States, who were not randomly assigned to groups. Han and Hung [ 66 ] recruited students from a junior high school in Taiwan, who were randomly assigned to groups. The study of Doxey et al. [ 86 ] was appraised as having low research quality, while that of Han and Hung [ 66 ] was appraised as having moderate research quality.

Original data of the studies examining the influence of indoor plants on academic achievement.

The heterogeneity test of the two studies investigating the influence of indoor plants on academic achievement revealed no significant difference ( p > 0.05), with I 2 = 0%, confirming low heterogeneity between the studies. A fixed-effect model was therefore applied. The pooled effect size (SMD) was 0.534, and the 95% confidence interval ranged from 0.167 to 0.901. The results indicated that the group with plants had significantly higher academic achievement ( p = 0.004) than the group without plants ( Table 17 ). The relative weight of Doxey et al. [ 86 ] was 68.95% and that of Han and Hung [ 66 ] was 31.05% ( Figure 6 ).

Forest plot of studies on the influence of indoor plants on academic achievement [ 66 , 86 ].

Heterogeneity test results of studies on the influence of indoor plants on academic achievement.

3.11. Response Time

Three papers examining the influence of indoor plants on response time, which was measured by various tasks with the unit of measurement as seconds or milliseconds, were included for the meta-analysis ( Table 18 ). These studies had a total of 749 participants. Among them, 374 participants were in the control group (without plants) and 375 in the experimental group (with plants). Nieuwenhuis et al. [ 58 ] recruited adult office workers in the United Kingdom, Kim et al. [ 77 ] recruited college students in Hong Kong, and Thatcher et al. [ 94 ] recruited adults in South Africa. Nieuwenhuis et al. [ 58 ] and Thatcher et al. [ 94 ] randomly assigned their participants to different groups, while Kim et al. [ 77 ] did not. All three papers were appraised as having moderate research quality.

Original data of the studies examining the influence of indoor plants on response time.

The heterogeneity test of the three studies investigating the influence of indoor plants on response time revealed a significant difference ( p < 0.05), with I 2 = 96.144%, confirming high heterogeneity among the studies. A random-effect model was therefore adopted. Given that great differences existed between the original data, SMD, rather than MD, was adopted. The pooled effect size (SMD) was −0.939, and the 95% confidence interval ranged from −2.208 to 0.401. The results indicated that the group with plants had less response time than did the group without plants. However, the difference was not significant ( p = 0.170) ( Table 19 ). The relative weight of the three studies was relatively similar, ranging from 34.89% to 32.02% ( Figure 7 ).

Forest plot of studies on the influence of indoor plants on response time [ 58 , 77 , 94 ].

Heterogeneity test results of studies on the influence of indoor plants on response time.

3.12. Risk of Bias across Studies

Because at least three records are required for the evaluation of publication bias, only the studies investigating the effects on DBP, EEG α waves, attention, and response time were suitable for testing the risk of bias across records in the meta-analyses. All funnel plots of these studies ( Figure 8 ) revealed a symmetric funnel, confirming the absence of publication bias. Furthermore, the linear Egger’s regressions all indicated no evidence of publication bias ( p > 0.374) ( Table 20 ).

Funnel plots. ( a ) DBP; ( b ) EEG α waves; ( c ) attention; ( d ) response time.

Results of linear Egger’s regressions test.

3.13. Additional Analysis

Sensitivity analysis was separately performed on records investigating the effects of indoor plants on physiological functions, including DBP and EEG α waves, and those on cognitive functions, including attention and response time, because at least three records are required. None of the pooled effect sizes changed notably when any of the studies was removed ( Figure 9 ). In summary, none of the pooled effect size values in the forest plots exceeded the 95% confidence interval of overall pooled effect size [ 95 ]. The results of the aforementioned four meta-analyses were therefore not sensitive; i.e., the results were stable and did not lead to a different conclusion if any of the included studies was deleted.

Forest plots of sensitivity analyses. ( a ) DBP [ 60 , 76 , 82 ]; ( b ) EEG α waves [ 56 , 72 , 81 ]; ( c ) attention [ 53 , 71 , 75 ]; ( d ) response time [ 58 , 77 , 94 ].

4. Discussion

The 42 records in the present systematic review provide a comprehensive perspective on the topic under investigation. Overall, the review suggests that indoor plants exerted a positive effect on objective functions in participants. Since 90.5% of the records are experiments, the above findings generally support a cause-and-effect relationship [ 49 ]. The findings on such matters, such as improved stress-reduction, increased task performance, and improved health, are in accordance with those of the previous reviews [ 31 , 36 , 40 , 45 ]. These various reviews together provide converging evidence that indoor plants are beneficial to humans, even though some reviews focused on self-reports, some on objective functions, and some did not distinguish subjective or objective responses. These findings, however, contrast with findings of no improvements in performance and productivity [ 41 ] and of no influences of indoor nature on adolescents [ 35 ]. This may be because of the differences in the measured outcomes of performance and/or functions and in the ages of the participants (cf. [ 17 ]). More studies of the effects of indoor plants on people are needed because only three systematic reviews and one meta-analysis are insufficient to draw conclusive evidence. Moreover, there are some overlapping studies between these reviews, which is not uncommon in reviews. This is also because some studies collected data on both self-reported perceptions and objectively measured responses.

4.1. Summary of Evidence

The meta-analyses covered only 16 records, consequently providing a more limited perspective than the systematic review. Nevertheless, it should be noted that synthesis findings are likely to be more reliable than those of single studies. Regarding the physiological functions, the meta-analyses further provided evidence synthesis that (1) participants exposed to indoor plants had significantly lower DBP values, which is related to excitement and arousal [ 96 ], than their counterparts exposed to no indoor plants; (2) participants exposed to indoor plants had greater EEG α waves, which is related to relaxation [ 97 ], than their counterparts, though the difference was not significant; and (3) participants exposed to indoor plants had greater EEG β waves, which is related to anxiety [ 69 ] and attention [ 98 ], than their counterparts. This difference was also not significant. It should be noted that whether the EEG wave patterns is a beneficial or an adverse function depends on the context [ 99 ]. Regarding cognitive functions, the meta-analyses further provided evidence synthesis that (1) participants exposed to indoor plants had lower attention than their counterparts, though the difference was not significant; (2) participants exposed to indoor plants had significantly higher academic achievement than their counterparts; and (3) participants exposed to indoor plants responded more quickly than their counterparts, though the difference was not significant.

Given that the pooled effect sizes of the records of DBP, EEG α waves, attention, and response time did not change notably when any record was deleted, the meta-analyses had high stability results; i.e., the removal of no study led to a different conclusion. Furthermore, the perfect homogeneity of the two studies on academic achievement provided reliable meta-analysis results (cf. [ 20 ]), although one of the included studies had low research quality, which was associated with risks of bias. Some of the results of the meta-analyses, however, were inconsistent, regardless of whether they reached significance. These included greater EEG α and β waves, and lower attention but higher academic achievement and quicker responses when exposed to indoor plants. Since there are three kinds of attention—working memory, cognitive flexibility, and attentional control—researchers should reach a consensus on which task to use to measure attention in order to have a more reliable evidence synthesis [ 19 , 20 ]. More studies of these subjects are needed.

The evidence synthesis of the relaxed physiology, as indicated by significantly lower DBP values when the participants were exposed to indoor plants than their counterparts, provided partial support to the SRT, which proposes that natural environment is helpful for recovery from stress [ 3 ], while that of the enhanced cognition, as indicated by significantly higher academic achievement when the participants exposed to indoor plants than their counterparts, provided partial support to the ART, which claims that the natural environment is beneficial to the restoration of directed attention [ 7 ]. Although different cultures may influence people’s perceptions of plants and even their functions in relation to plants (cf. [ 3 ]), there appears to be no research on these issues. Nevertheless, the evidence synthesis regarding human functions of this study seems not to be influenced by cultures. The evidence synthesis of relaxed physiology comes from the studies recruiting participants in the South Korea [ 82 ], China [ 60 ], and Taiwan [ 76 ]. Although these three studies had a significant heterogeneity (I 2 = 97.554%), the removal of any study did not change the results. Moreover, the evidence synthesis of enhanced cognition comes from the studies recruiting participants in the US [ 86 ] and Taiwan [ 66 ] but had a perfect homogeneity (I 2 = 0%). Nevertheless, more studies are needed to explore the influences of different cultures on peoples’ perceptions and functions with respect to plants.

As mentioned in the previous section concerning the risk of bias within studies, the records suffered, in general, five major risks of bias. First, noncompliance with an ITT analysis might result in unduly liberal estimate of the treatment effect [ 100 ]. Second, results obtained from unrepresentative participants might prevent observed effects from being generalizable to a larger population [ 49 ], but generalizability is improved more by many heterogeneous small experiments than by only a few large experiments [ 50 ]. Third, when outcome assessors were aware of participant allocation, outcomes might be assessed differently [ 101 ]. Fourth, statistical power not being reported might increase Type II errors: the acceptance of a null hypothesis that is actually false [ 102 ]. Fifth, the lack of appropriate randomization procedures and random allocation to groups might introduce bias [ 103 ].

Moreover, the records on the physiological and cognitive functions for the meta-analyses were susceptible to other risks of bias. Inclusion and/or exclusion criteria of participants not being reported [ 53 , 58 , 66 , 71 , 77 , 86 , 94 ] might miss the target population and/or might bias the research results [ 104 ]. Baseline measures not taken before the intervention [ 58 , 72 , 76 , 81 , 86 , 94 ] lacked a point of reference to gauge how effective the intervention is [ 49 ]. Inappropriate statistical analysis methods for study design, such as repeated-measures or within-subjects design not using repeated-measures or dependent-sample analyses [ 72 , 81 ], led to incorrect results. Not blinding participants to research questions [ 82 ] might affect their responses [ 105 ]. Lack of individual level allocation [ 58 , 81 , 86 ], in which each participant did not have an equal opportunity of being assigned to groups, might result in incomparable groups before intervention [ 50 ]. Inconsistency of intervention (within and between groups) was an issue in several studies as the intervention included more than one treatment [ 53 , 56 , 58 , 66 , 71 , 72 , 77 , 81 , 94 ], such as various plant colors.

Some studies found gender differences regarding physiological mobilization [ 57 , 62 , 69 , 83 ] and cognitive functions [ 70 , 71 ]. Such findings suggest that taking gender into consideration when investigating the effects of indoor plants is important, since males and females may have differing physiological and psychological responses (cf. [ 24 ]). Some of the records also showed different effects of plants with flowers and without flowers on physiology [ 57 , 69 , 83 ] and behavior [ 85 ]. Taking flowers and their colors and even leaf colors into account, therefore, when examining the effects of indoor plants is necessary. Moreover, most of the studies investigated the effect of only single exposure to indoor plants. Although a few studies examined the long-term effects [ 57 , 65 , 66 , 67 , 76 , 86 ], they did not scrutinize the specific effect of exposure time and/or frequency, nor did they include studies considering the influence of distance between plant and participant.

4.2. Limitations

Only journal articles were included in the review and meta-analyses, whereas grey literature was excluded. Therefore, some publication bias may have been involved [ 43 ]. There was a chance of positive [ 86 ] and/or small [ 75 , 81 , 82 ] studies being overrepresented, thus biasing the evidence synthesis. In general, studies with negative findings are less published than positive findings [ 106 ], which may give a distorted image of what is really known about a subject [ 107 , 108 ]. However, the results of DBP, EEG α waves, attention, and response time all indicated no evidence of publication bias. Furthermore, only a few records were included for the meta-analyses. Though conducting a meta-analysis with two or three studies is acceptable, it is not ideal. Since some of the 42 papers were published a long time ago, their authors could not locate the original data on means and standard deviations. Some authors could not even be reached. Additionally, five of the six meta-analyses had a very high heterogeneity (I 2 > 82%), which is associated with low reliability results [ 109 ]. This may be because of the diversity in the recruited participants, applied interventions, measured outcomes, and adopted study designs (cf. [ 109 ]). Additionally, because there were only two or three records for each of the meta-analyses, subgroup analyses, meta-regression analyses, moderating factors (gender, plant quantity, exposure duration, distance to plants, room climate, and room size), and further analyses for the risk of bias could not be conducted. Nevertheless, the results of DBP, EEG α waves, attention, and response time showed no publication bias. Moreover, because of the lack of original data on means and standard deviations or the insufficient number of studies, a meta-analysis on the effects of indoor plants on objective functions in behavior (e.g., pain tolerance and misconduct), health (sick leave, pain killer consumption, and hospitalizations), physiology (EDA, heart rate, respiration rate, and body temperature), and cognition (productivity and reaction) could not be performed. Finally, the studies included for the systematic review and those for the meta-analyses, in general, had moderate research quality (45.3% for those in the review, and 48.0% for those in the meta-analyses; [ 19 ]). Thus, high-quality research was lacking ( Table 5 and Table 6 ).

4.3. Suggestions

Future studies should recruit more people living in the equatorial area and the Global South in general and Africans in specific, preferably not college students ( Table 2 ). Background information of the participants, such as gender, age, occupation, ethnicity, health status, and number before, during, and after the research, should be provided. Study designs should use more field experiments conducted in real-world indoor environments rather than laboratories in order to improve ecological validity and still maintain sound internal validity [ 50 ]. More high-quality research is required, such as research involving experiments that follow the Consolidated Standards of Reporting Trials (CONSORT; [ 110 ]), nonrandom experiments that follow the Transparent Reporting of Evaluations with Nonrandomized Designs (TREND; [ 111 ]), and, in general, the Publication Manual of the American Psychological Association [ 112 ].

Given that indoor plants are the intervention itself, indoor plants are associated with the construct validity of the research [ 31 ] in which plant quantity, plant–participant distance, exposure time, and exposure frequency all affect the dose–response relationship (cf. [ 113 , 114 , 115 ]). Accordingly, we suggest that future studies adopt standardized measurements of the plant quantity, such as the volume percentage of the plants in an indoor environment or the visible greenness rate. The volume percentage of the plants has been used in the included studies [ 53 , 67 ], while the visible greenness rate has also been used in previous studies [ 38 ]. The visible greenness rate concerns the percentage of the plants seen by human eyes, which is an objective measurement of plants in a three-dimensional space in the field of vision [ 116 ]. Consideration of plant quantity, exposure time, frequency, and distance may assist researchers to examine rigorously how exposure to indoor plants in terms of one event or short-term period or multiple events or long-term periods affects the objective functions of individuals by means of a dose–response or exposure–outcome relationship.

In addition to the dose of and/or exposure to the indoor plants, gender difference, flower colors, flower shapes, plant colors, plant shapes [ 57 , 62 , 69 , 70 , 71 , 83 , 85 , 88 , 89 ], and cultural influences should also be considered. Furthermore, the physiology of plants, including such factors as their roots and microorganisms [ 117 , 118 ], photosynthesis, adsorption, respiration, and evapotranspiration, which are helpful for air quality and microclimate [ 40 , 47 , 119 ], may need to be considered. Similarly, researchers should also report more detailed data on room climate, room size, light condition ( Table 3 and Table 4 ), and seasonal condition, because air quality, temperature, relative humidity, light, and season also affect human comfort, performance, and health [ 120 ]. The mechanisms of and/or pathways to the effects of indoor plants on human functions also await exploration. Furthermore, indoor plants are mostly studied for their individual performances rather than as a combination. The research into the effect of plants usually focuses on the effects of single plants of different species in different conditions. Attention should further be placed on species that can cohabitate together, thus compensating each other’s needs and recreating the basic forms of symbiosis [ 121 ].

Finally, if the number of studies remains inadequate during future analyses, various aspects of human functions may be integrated into physiology (with respect to the sympathetic nervous system or parasympathetic nervous system), cognition (regarding participants’ reaction time and accuracy rate), health (in terms of illness and recovery), and behavior (either positive or negative). In that manner, the standardized mean differences (SMDs) of the function data could be adopted to conduct more rigorous meta-analyses, subgroup analyses, meta-regression analyses, and moderating factors. In contrast to self-reported measures, objective outcome measures lead to fewer reliability and validity concerns (cf. [ 122 ]) and risk of bias [ 123 ]. Nevertheless, compare and contrast of self-reported measures and objective outcome measures can provide interesting results and can be an advantage of such endeavor (c.f. [ 124 , 125 , 126 ]).

5. Conclusions

The systematic review of 42 records showed that indoor plants affect participants’ objective functions positively, particularly in terms of relaxed physiology and improved cognition. The meta-analyses further provided the evidence synthesis that indoor plants could significantly benefit participants’ SBP and academic achievement, which supported the SRT and ART. The records for the abovementioned meta-analyses, however, were limited, at only three studies for the SBP and two studies for the academic achievement. The evidence synthesis should be interpreted with caution. In brief, the systematic review concluded that, in general, people have better functions with the presence of indoor plants than the absence of indoor plants, and the meta-analyses concluded that, in specific, people have significantly lower SBP and significantly greater academic achievement when indoor plants are present than when indoor plants are not present, though with limited evidence synthesis. Since this study was the first meta-analyses of the effects of indoor plants on people’s functions, however, the findings may help the general public, environmental designers, and planners and policy makers to conduct appropriate assessments and to implement measures to improve psycho-physiological health and productivity (i.e., relaxed physiology and enhanced cognition) of habitants. The estimated productivity decrease caused by sick building syndrome, which is “a medical condition in which people in a building suffer from symptoms of illness or feeling unwell for no apparent reason” [ 127 ], in American office workers, for example, was 2%, for an annual cost of roughly 60 billion USD [ 128 ]. Furthermore, poor indoor air quality decreases workplace productivity by 10–15% [ 129 ]. The integration of plants as a building service is viable. A combination of indoor plants and ventilation technology provides enhanced efficiency and effectiveness of air purification [ 130 , 131 ]. Not only are green spaces needed in cities, but also plants are needed in buildings for people’s health and well-being. For the sake of people’s effective daily functions, indoor plants should be among the important elements of the healthy city, particularly in terms of their easy applicability and accessibility.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/ijerph19127454/s1 , Table S1: The full search strings; Table S2: Full-text excluded, with reason for exclusion.

Funding Statement

This research was funded by the Ministry of Science and Technology, grant number MOST 107-2410-H-167-008-MY2.

Author Contributions

Conceptualization, K.-T.H.; methodology, K.-T.H.; validation, K.-T.H.; formal analysis, K.-T.H. and L.-W.R.; investigation, K.-T.H. and L.-W.R.; resources, K.-T.H.; data curation, K.-T.H., L.-W.R. and L.-S.L.; writing—original draft preparation, K.-T.H.; writing—review and editing, K.-T.H.; visualization, L.-W.R. and L.-S.L.; supervision, K.-T.H.; project administration, K.-T.H.; funding acquisition, K.-T.H. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Data availability statement, conflicts of interest.

The authors declare no conflict of interest.

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Plant Taxonomy: A Historical Perspective, Current Challenges, and Perspectives

• First Online: 11 December 2020

Cite this protocol

• Germinal Rouhan 3 &
• Myriam Gaudeul 3  

Part of the book series: Methods in Molecular Biology ((MIMB,volume 2222))

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Taxonomy is the science that explores, describes, names, and classifies all organisms. In this introductory chapter, we highlight the major historical steps in the elaboration of this science, which provides baseline data for all fields of biology and plays a vital role for society but is also an independent, complex, and sound hypothesis-driven scientific discipline.

In a first part, we underline that plant taxonomy is one of the earliest scientific disciplines that emerged thousands of years ago, even before the important contributions of the Greeks and Romans (e.g., Theophrastus, Pliny the Elder, and Dioscorides). In the fifteenth–sixteenth centuries, plant taxonomy benefited from the Great Navigations, the invention of the printing press, the creation of botanic gardens, and the use of the drying technique to preserve plant specimens. In parallel with the growing body of morpho-anatomical data, subsequent major steps in the history of plant taxonomy include the emergence of the concept of natural classification , the adoption of the binomial naming system (with the major role of Linnaeus) and other universal rules for the naming of plants, the formulation of the principle of subordination of characters, and the advent of the evolutionary thought. More recently, the cladistic theory (initiated by Hennig) and the rapid advances in DNA technologies allowed to infer phylogenies and to propose true natural, genealogy-based classifications.

In a second part, we put the emphasis on the challenges that plant taxonomy faces nowadays. The still very incomplete taxonomic knowledge of the worldwide flora (the so-called taxonomic impediment) is seriously hampering conservation efforts that are especially crucial as biodiversity has entered its sixth extinction crisis. It appears mainly due to insufficient funding, lack of taxonomic expertise, and lack of communication and coordination. We then review recent initiatives to overcome these limitations and to anticipate how taxonomy should and could evolve. In particular, the use of molecular data has been era-splitting for taxonomy and may allow an accelerated pace of species discovery. We examine both strengths and limitations of such techniques in comparison to morphology-based investigations, we give broad recommendations on the use of molecular tools for plant taxonomy, and we highlight the need for an integrative taxonomy based on evidence from multiple sources.

Taxonomy can justly be called the pioneering exploration of life on a little known planet. —Wilson (2004). The goal of discovering, describing, and classifying the species of our planet assuredly qualifies as big science . —Wheeler et al. (2004).

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Rouhan, G., Gaudeul, M. (2021). Plant Taxonomy: A Historical Perspective, Current Challenges, and Perspectives. In: Besse, P. (eds) Molecular Plant Taxonomy. Methods in Molecular Biology, vol 2222. Humana, New York, NY. https://doi.org/10.1007/978-1-0716-0997-2_1

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Published : 11 December 2020

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The Science of Plants

Tom Michaels, Saint Paul, MN

Emily Hoover, Saint Paul, MN

Laura Irish, Saint Paul, MN

Copyright Year: 2022

ISBN 13: 9781946135872

Publisher: University of Minnesota Libraries Publishing

Language: English

Formats Available

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Learn more about reviews.

Reviewed by Paula Mejia Velasquez, Adjunct Professor, Leeward Community College on 12/8/22

This book is a great resource for an introductory-level class on Horticulture or botany, covering most of the topics usually addressed in a class at the undergrad level. Some topics are explained in more detail than others, but all the topics... read more

Comprehensiveness rating: 4 see less

This book is a great resource for an introductory-level class on Horticulture or botany, covering most of the topics usually addressed in a class at the undergrad level. Some topics are explained in more detail than others, but all the topics presented in the book are well explained. An important topic that is not included in the book is ecology, explaining different ways that plants interact with other organisms (e.g. animals, plants, fungi).

Content Accuracy rating: 5

The content of the book appears accurate, and the topics are presented in a neutral, not biased way.

Relevance/Longevity rating: 5

The topics covered in the book are relevant for an introductory plant science class at an undergrad level. In terms of longevity, most of the material should still be relevant in the long term, but other topics, like taxonomy, would probably need to be updated every so often.

Clarity rating: 5

The book is easy to follow and read, at a level that is accessible and understandable for undergrad students. A list of terms or glossary is included in each chapter and at the end of the book, this helps students that need more explanation on a term.

Consistency rating: 5

The book is consistent from beginning to end, presenting a similar writing style and format.

Modularity rating: 5

The organization of the chapters and the subunits is clear and consistent. Individual chapters or subunits can be found easily on the chapter outline, making it easy to alter the order of the book content based on teaching preferences.

Organization/Structure/Flow rating: 2

Each chapter consists of a brief introduction, learning objectives, the topic per se, and a glossary. This structure is similar to most textbooks and I think it works great. However, I had a hard time with the order that the topics are presented in this book. In my opinion, the organization of the chapters could follow a different order to improve the flow of the book. There are several concepts/topics in the book that are grouped with concepts/topics that do not seem to be closely related, and that maybe would fit better under other more related chapters. For example, flower morphology is grouped in a chapter with meristems, plant taxonomy is grouped with seed germination, and plant growth is grouped with inflorescences. It would probably make more sense to group flower morphology with inflorescences, and meristems with plant growth. In a specific example, seed germination is presented in Chapter 2 as section 2.2, but a more comprehensive chapter on seeds is included in Chapter 9. I think the seed germination section would be a better fit for Chapter 9, and leave Chapter 2 as a taxonomic chapter.

Interface rating: 4

The textbook is available in different formats, including pdf, word, xml, ebook, and online. I explored the online and pdf versions and found them easy to navigate. The online version includes short videos that expand on some topics, as well as embedded h5p interactive activities to test comprehension and increase student engagement. The pdf version on the other hand does not have the videos or interactive activities embedded, instead, it provides links to them. However, some of the links provided do not work (e.g. links on pages 12 -13). I would recommend using the online version of the book.

Grammatical Errors rating: 5

The text contains no significant amount of grammatical errors.

Cultural Relevance rating: 5

I did not find the book to be culturally insensitive or offensive. It is mainly focused on plants found in northern temperate areas. Including some tropical examples could make this book more attractive to a wider audience.

This book does a great job of covering and explaining basic plant and horticultural science concepts that are typically included in an introductory-level botany or horticulture class. I really liked that it includes videos, a glossary, interactive activities (i.e. h5p), and other supplementary materials (i.e. review questions and Quizlet flashcards), as I think they are great tools to complement the content of the book and engage students. The book is easy to read, each chapter includes specific learning outcomes, a chapter outline, a summary, and review questions. I disagree with the order the topics are presented, but each instructor could easily address this by assigning the chapters in a different order.

Table of Contents

Chapter 1: Plants in our Lives

1.1 What is horticulture?

1.2 Science and Experimentation

1.3 Plant Parts we Eat

Chapter 1: Terms

Chapter 2: Taxonomy and Seed Germination

2.1 Plant Taxonomy

2.2 Introduction to Seed Germination

Chapter 2: Terms

Chapter 3: How Plants Grow, Part 1

Chapter 3: Terms

Chapter 4: How Plants Grow, Part 2

4.1 Growth Patterns and Inflorescences

4.2 Plant Hormones

Chapter 4: Terms

Chapter 5: Inside Plants

5.1 Inside Leaves

5.2 Inside Stems

5.3 Inside Roots

Chapter 5: Terms

Chapter 6: Cells, Tissues, and Woody Growth

6.1 Plant Cells and Tissues

6.2 Woody Growth

Chapter 6: Terms

Chapter 7: Meristems and Flowers

7.1 Meristem Morphology

7.2 Flower Morphology

Chapter 7: Terms

Chapter 8: Fruit

8.1 Fruit Morphology

Chapter 8: Terms

Chapter 9: Seeds

9.1 Seed Morphology

9.2 Seed Physiology

Chapter 9: Terms

Chapter 10: Grafting

10.1 Grafts and Wounds

10.2 Unique Storage Organs

Chapter 10: Terms

Chapter 11: Water and Light

11.1 Plants and Water

11.2 Light and Photosynthesis

Chapter 11: Terms

Chapter 12: Soils, Fertility, and Plant Growth

12.1 Soils, Fertility, and Plant Growth

Chapter 12: Terms

Chapter 13: Sexual Reproduction

13.2 Mitosis

13.3 Meiosis

Chapter 13: Terms

Chapter 14: Variation and Plant Breeding

14.1 Gametogenesis

14.2 Inheritance of Big Differences

14.3 Linkage and Inheritance of Small Differences

14.4 Plant Breeding

Chapter 14: Terms

Chapter 15: Invasive plants and GMOs

15.1 Invasive plants

Chapter 15: Terms

Glossary of Terms

Ancillary Material

About the book.

An approachable guide to the fundamentals of plant science. Created for horticulture students, gardeners, science teachers, and anyone interested in understanding plants and how they grow. This is the required text for HORT 1001/6001 Plant Propagation at the University of Minnesota Department of Horticultural Science.

About the Contributors

Dr. Michaels enjoys investigating phenotypic variations among plants, determining whether they have a genetic basis, and using them to select for improved cultivars. His current work focuses on dry edible beans, industrial hemp, sweet sorghum, and lettuce for organic and small farm production systems. He is passionate about developing and delivering effective undergraduate learning experiences for his students in face-to-face and online formats.

Dr. Hoover’s research examines production methodologies for producing fruit crops with sustainable methods, emphasizing practices that are gentle on the environment. She and her colleagues have developed systems for minimizing weed pressure in June- bearing strawberries and for producing day-neutral strawberries in cold climates. She is also part of the international research group  NC140 , which studies the winter hardiness of apple rootstocks. She was appointed Head of the Department of Horticultural Science at the University of Minnesota (UMN) in 2009, and leads a diverse group of faculty and staff who work to produce knowledge on a wide range of plant species, including traditional horticultural plants, fruits, vegetables, and flowers

Ms. Irish received her BS in Horticulture, with an emphasis in public horticulture, in 2015. She went directly into her master’s program, working on a collaboration between the Iowa SNAP-Ed and Master Gardener programs that involved working with master gardeners on food security projects across the state. As both an undergrad and a graduate student she served as a teaching assistant for the introductory horticulture course labs, the hands-on horticulture lab, and the upper-level plant propagation course. She teaches the plant propagation labs at UMN and advises the Horticulture Club.

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