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[[Category:植物|*]]
[[Category:植物相]]
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{{For|an explanation of similar terms|Viridiplantae|Green algae}}
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{{Taxobox
| name = Plants
| fossil_range = {{long fossil range|Mesoproterozoic|present}}
| image = Diversity of plants image version 5.png
| image_caption =
| domain = [[Eukaryota]]
| unranked_regnum = [[Archaeplastida]]
| regnum = '''Plantae'''
| regnum_authority = ''sensu'' Copeland, 1956
| subdivision_ranks = Divisions
| subdivision = * [[Chlorokybophyceae|Chlorokybophyta]]
* [[Mesostigmatophyceae|Mesostigmatophyta]]
* '''Chlorobionta''' <small>Kenrick & Crane 1997</small>
** [[Chlorophyta]]
* '''[[Streptophyta|Streptobionta]]''' <small>Kenrick & Crane 1997</small>
** [[Klebsormidiophyceae]]
** [[Charophyta]] (stoneworts)
** ?[[Chaetosphaeridiales]]
** [[Coleochaetophyceae|Coleochaetophyta]]
** [[Zygnematophyceae|Zygnematophyta]]
** [[Embryophyta|Embryobiotes]] <small>Kenrick & Crane 1997</small>(land plants)
*** [[Marchantiophyta]]
*** [[Moss|Bryophyta]]
*** [[Anthocerotophyta]]
*** †[[Horneophytopsida|Horneophyta]]
*** †[[Aglaophyton|Aglaophyta]]
*** [[Tracheophyta]] (vascular plants)
| synonyms =
{{hidden begin}}
* [[Viridiplantae]] <small>Cavalier-Smith 1981</small><ref name=CavalierSmith1981>{{cite journal |first=T. |last=Cavalier-Smith|date=1981|title=Eukaryote kingdoms: Seven or nine?|journal=BioSystems|volume=14|issue=3–4|pages=461–481|doi=10.1016/0303-2647(81)90050-2|pmid=7337818}}</ref>
* Chlorobionta <small>Jeffrey 1982, emend. Bremer 1985, emend. Lewis and McCourt 2004</small><ref name=LewisMcCourt>{{cite journal|last1=Lewis|first1=L.A.|first2=R.M.|last2=McCourt|date=2004|title=Green algae and the origin of land plants|journal=American Journal of Botany|volume=91|pages=1535–1556|doi=10.3732/ajb.91.10.1535|pmid=21652308}}</ref>
* Chlorobiota <small>Kenrick and Crane 1997</small><ref name=KenrickCrane1997>{{cite book |last1=Kenrick|first1=Paul|last2=Crane|first2=Peter R.|date=1997|title=The origin and early diversification of land plants: A cladistic study|location=Washington, D. C.|publisher=Smithsonian Institution Press|isbn=1-56098-730-8}}</ref>
* Chloroplastida <small>Adl et al., 2005 </small><ref name=Adl>{{cite journal|authors=Adl, S.M.| date=2005|title=The new higher level classification of eukaryotes with emphasis on the taxonomy of protists|journal=Journal of Eukaryote Microbiology|volume= 52|pages=399–451|doi=10.1111/j.1550-7408.2005.00053.x |display-authors=etal|pmid=16248873}}</ref>
* Phyta <small>Barkley 1939</small> emend. <small>Holt & Uidica 2007</small>
* Cormophyta <small>Endlicher, 1836</small>
* Cormobionta <small>Rothmaler, 1948</small>
* Euplanta <small>Barkley, 1949</small>
* Telomobionta <small>Takhtajan, 1964</small>
* Embryobionta <small>Cronquist et al., 1966</small>
* Metaphyta <small>Whittaker, 1969</small>
{{hidden end}}
}}
'''Plants''' are mainly [[multicellular organism|multicellular]], predominantly [[photosynthesis|photosynthetic]] [[eukaryote]]s of the [[Kingdom (biology)|kingdom]] '''Plantae'''. They form the [[clade]] [[Viridiplantae]] (Latin for "green plants") that includes the [[flowering plant]]s, [[conifer]]s and other [[gymnosperm]]s, [[fern]]s and [[Fern ally|their allies]], [[hornwort]]s, [[Marchantiophyta|liverwort]]s, [[moss]]es and the [[green algae]], and excludes the [[Rhodophyta|red]] and [[Phaeophyceae|brown algae]]. Historically, plants were treated as one of two kingdoms including all living things that were not [[animal]]s, and all [[algae]] and [[fungus|fungi]] were treated as plants. However, all current definitions of Plantae exclude the fungi and some algae, as well as the [[prokaryote]]s (the [[archaea]] and [[bacteria]]).
Green plants obtain most of their energy from [[sunlight]] via [[photosynthesis]] by primary [[chloroplast]]s that are derived from [[endosymbiosis]] with [[cyanobacteria]]. Their chloroplasts contain [[chlorophyll]]s a and b, which gives them their green color. Some plants are [[Parasitic plant|parasitic]] or [[mycotroph]]ic and may lose the ability to produce normal amounts of chlorophyll or to photosynthesize. Plants are characterized by [[sexual reproduction]] and [[alternation of generations]], although [[asexual reproduction]] is also common.
There are about 300–315 thousand [[species]] of plants, of which the great majority, some 260–290 thousand, are [[seed plant]]s (see the [[#Diversity|table below]]).<ref name="IUCNdata">{{cite web |title= Numbers of threatened species by major groups of organisms (1996–2010) |publisher= International Union for Conservation of Nature |date= 11 March 2010 |url= http://www.iucnredlist.org/documents/summarystatistics/2010_1RL_Stats_Table_1.pdf |format= PDF }}</ref> Green plants provide a substantial proportion of the world's molecular oxygen<ref name=behrenfeld>{{cite journal | last=Field | first=C.B. |author2=Behrenfeld, M.J. |author3=Randerson, J.T. |author4=Falkowski, P. | year=1998 | title=Primary production of the biosphere: Integrating terrestrial and oceanic components | journal=[[Science (journal)|Science]] | volume=281 | pages=237–240 | doi=10.1126/science.281.5374.237 | pmid=9657713 | issue=5374 |bibcode = 1998Sci...281..237F }}</ref> and are the basis of most of Earth's ecosystems, especially on land. Plants that produce [[grain]], [[fruit]] and [[vegetable]]s form humankind's basic foodstuffs, and have been [[domestication|domesticated]] for millennia. Plants have many [[Plants in culture|cultural]] and other uses as ornaments, [[building materials]], [[writing material]] and in great variety, they have been the source of [[Pharmaceutical drug|medicines]] and [[drug]]s. The scientific study of plants is known as [[botany]], a branch of [[biology]].
== Definition ==
All living things were traditionally placed into one of two groups, plants and animals. This classification may date from [[Aristotle]] (384 BC – 322 BC), who made the distincton between plants, which generally do not move, and animals, which often are mobile to catch their food. Much later, when [[Carl Linnaeus|Linnaeus]] (1707–1778) created the basis of the modern system of [[scientific classification]], these two groups became the [[kingdom (biology)|kingdoms]] Vegetabilia (later Metaphyta or Plantae) and [[Animalia]] (also called Metazoa). Since then, it has become clear that the plant kingdom as originally defined included several unrelated groups, and the [[fungus|fungi]] and several groups of [[algae]] were removed to new kingdoms. However, these organisms are still often considered plants, particularly in popular contexts.
The term "plant" generally implies the possession of the following traits: multicellularity, possession of cell walls containing [[cellulose]] and the ability to carry out photosynthesis with primary chloroplasts.<ref name="urlplant[2] – Definition from the Merriam-Webster Online Dictionary">{{cite web |url=http://www.merriam-webster.com/dictionary/plant%5B2%5D |title=plant[2] – Definition from the Merriam-Webster Online Dictionary |work= |accessdate=2009-03-25}}</ref><ref name="urlplant (life form) -- Britannica Online Encyclopedia">{{cite web |url=http://www.britannica.com/EBchecked/topic/463192/plant |title=plant (life form) -- Britannica Online Encyclopedia |work= |accessdate=2009-03-25}}</ref>
=== Current definitions of Plantae{{anchor|Current definitions of Plantae}} ===
When the name Plantae or plant is applied to a specific group of organisms or [[taxon]], it usually refers to one of four concepts. From least to most inclusive, these four groupings are:
{| class="wikitable"
|-
! Name(s)
! Scope
! Description
|-
| [[Embryophyte|Land plants]], also known as Embryophyta
| Plantae ''[[Glossary of botanical terms#sensu strictissimo|sensu strictissimo]]''
| '''Plants in the strictest sense''' include the [[liverworts]], [[hornworts]], [[mosses]], and [[vascular plant]]s, as well as fossil plants similar to these surviving groups (e.g., Metaphyta <small>Whittaker, 1969</small>,<ref name="ib.usp.br">{{cite journal | last1 = Whittaker | first1 = R. H. | year = 1969 | title = New concepts of kingdoms or organisms | url = http://www.ib.usp.br/inter/0410113/downloads/Whittaker_1969.pdf | format = PDF | journal = Science | volume = 163 | issue = 3863| pages = 150–160 | doi=10.1126/science.163.3863.150 | pmid=5762760| bibcode = 1969Sci...163..150W }}</ref> Plantae <small>[[Lynn Margulis|Margulis]], 1971</small><ref>{{cite journal | last1 = Margulis | first1 = L | year = 1971 | title = Whittaker's five kingdoms of organisms: minor revisions suggested by considerations of the origin of mitosis | url = | journal = Evolution | volume = 25 | issue = | pages = 242–245 | doi=10.2307/2406516}}</ref>).
|-
| '''Green plants''', also known as '''[[Viridiplantae]]''', '''Viridiphyta''' or '''Chlorobionta'''
| Plantae ''[[Glossary of botanical terms#sensu stricto|sensu stricto]]''
| '''Plants in a strict sense''' include the [[green algae]], and land plants that emerged within them, including [[stonewort]]s. The names given to these groups vary considerably {{as of|2011|July|lc=yes}}. Viridiplantae encompass a group of organisms that have [[cellulose]] in their [[cell wall]]s, possess [[chlorophyll]]s ''a'' and ''b'' and have [[plastid]]s that are bound by only two membranes that are capable of storing starch. It is this [[clade]] that is mainly the subject of this article (e.g., Plantae <small>[[Herbert Copeland|Copeland]], 1956</small><ref>Copeland, H. F. (1956). The Classification of Lower Organisms. Palo Alto: Pacific Books, p. 6, [https://archive.org/details/classificationof00cope].</ref>).
|-
| [[Archaeplastida]], also known as Plastida or Primoplantae
| Plantae ''[[Glossary of botanical terms#sensu lato|sensu lato]]''
| '''Plants in a broad sense''' comprise the green plants listed above plus the red algae ([[Rhodophyta]]) and the glaucophyte algae ([[Glaucophyta]] that store [[Floridean starch]] outside the plastids (in the cytoplasm). This clade includes all of the organisms that eons ago acquired their [[chloroplast]]s directly by engulfing [[cyanobacteria]] (e.g., Plantae <small>Cavalier-Smith, 1981</small><ref>{{cite journal | last1 = Cavalier-Smith | first1 = T. | year = 1981 | title = Eukaryote Kingdoms: Seven or Nine?". | url = | journal = BioSystems | volume = 14 | issue = 3–4| pages = 461–481 | doi=10.1016/0303-2647(81)90050-2 | pmid=7337818}}</ref>).
|-
| [[List of systems of plant taxonomy|Old definitions of plant]] (obsolete)
| Plantae ''[[Glossary of botanical terms#sensu amplo|sensu amplo]]''
| '''Plants in the widest sense''' refers to older, obsolete classifications that placed diverse algae, fungi or bacteria in Plantae (e.g., Plantae or Vegetabilia <small>Linnaeus</small>,<ref>Linnaeus, C. (1751). ''[https://books.google.com/books?id=D18OAAAAQAAJ&pg=PA37 Philosophia botanica]'', 1st ed., p. 37.</ref> Plantae <small>Haeckel 1866</small>,<ref>{{cite book |author= Haeckel, E. |year= 1866 |title= Generale Morphologie der Organismen |publisher= Verlag von Georg Reimer |location= Berlin |pages= vol.1: i–xxxii, 1–574, pls I–II; vol. 2: i–clx, 1–462, pls I–VIII}}</ref> Metaphyta <small>Haeckel, 1894</small>,<ref>Haeckel, E. (1894). ''[https://archive.org/details/systematischephy01haec Die systematische Phylogenie]''.</ref> Plantae <small>Whittaker, 1969</small><ref name="ib.usp.br" />).
|}
Another way of looking at the relationships between the different groups that have been called "plants" is through a [[cladogram]], which shows their evolutionary relationships. These are not yet completely settled, but one accepted relationship between the three groups described above is shown below.<ref>Based on {{Citation|last=Rogozin |first=I.B. |last2=Basu |first2=M.K.|last3=Csürös |first3=M.|last4=Koonin|first4=E.V. |year=2009 |title=Analysis of Rare Genomic Changes Does Not Support the Unikont–Bikont Phylogeny and Suggests Cyanobacterial Symbiosis as the Point of Primary Radiation of Eukaryotes |journal=Genome Biology and Evolution|pmid=20333181 |volume=1|pmc=2817406|pages=99–113 |doi=10.1093/gbe/evp011 |lastauthoramp=yes}} and {{Citation |last=Becker |first=B. |last2=Marin |first2=B. |year=2009 |title=Streptophyte algae and the origin of embryophytes |journal=Annals of Botany |volume=103 |issue=7 |pages=999–1004 |doi=10.1093/aob/mcp044 |lastauthoramp=yes |pmid=19273476 |pmc=2707909}}; see also the slightly different cladogram in {{Citation |last=Lewis |first=Louise A. |last2=McCourt |first2=R.M. |year=2004 |title=Green algae and the origin of land plants |journal=Am. J. Bot. |volume=91 |issue=10 |pages=1535–1556 |doi=10.3732/ajb.91.10.1535 |lastauthoramp=yes |pmid=21652308}}</ref><ref>{{Cite journal|title = Estimating the timing of early eukaryotic diversification with multigene molecular clocks|url = http://www.pnas.org/content/108/33/13624|journal = Proceedings of the National Academy of Sciences|date = 16 August 2011|issn = 0027-8424|pmc = 3158185|pmid = 21810989|pages = 13624–13629|volume = 108|issue = 33|doi = 10.1073/pnas.1110633108|first = Laura Wegener|last = Parfrey|first2 = Daniel J. G.|last2 = Lahr|first3 = Andrew H.|last3 = Knoll|first4 = Laura A.|last4 = Katz|bibcode = 2011PNAS..10813624P}}</ref><ref>{{Cite journal|title = Bacterial proteins pinpoint a single eukaryotic root|url = http://www.pnas.org/content/112/7/E693|journal = Proceedings of the National Academy of Sciences|date = 17 February 2015|issn = 0027-8424|pmc = 4343179|pmid = 25646484|pages = E693-E699|volume = 112|issue = 7|doi = 10.1073/pnas.1420657112|first = Romain|last = Derelle|first2 = Guifré|last2 = Torruella|first3 = Vladimír|last3 = Klimeš|first4 = Henner|last4 = Brinkmann|first5 = Eunsoo|last5 = Kim|first6 = Čestmír|last6 = Vlček|first7 = B. Franz|last7 = Lang|first8 = Marek|last8 = Eliáš|bibcode = 2015PNAS..112E.693D}}</ref><ref>{{Cite journal|title = The Glaucophyta: the blue-green plants in a nutshell|url = https://dx.doi.org/10.5586/asbp.2015.020|journal = Acta Societatis Botanicorum Poloniae|date = 1 January 2015|volume = 84|issue = 2|doi = 10.5586/asbp.2015.020|first = Christopher|last = Jackson|first2 = Susan|last2 = Clayden|first3 = Adrian|last3 = Reyes-Prieto|pages=149–165}}</ref><ref name="Sánchez-Baracaldo E7737–E7745">{{Cite journal|last=Sánchez-Baracaldo|first=Patricia|last2=Raven|first2=John A.|last3=Pisani|first3=Davide|last4=Knoll|first4=Andrew H.|date=2017-09-12|title=Early photosynthetic eukaryotes inhabited low-salinity habitats|url=http://www.pnas.org/lookup/doi/10.1073/pnas.1620089114|journal=Proceedings of the National Academy of Sciences|volume=114|issue=37|pages=E7737–E7745|doi=10.1073/pnas.1620089114}}</ref><ref>{{Cite journal|last=Gitzendanner|first=Matthew A.|last2=Soltis|first2=Pamela S.|last3=Wong|first3=Gane K.-S.|last4=Ruhfel|first4=Brad R.|last5=Soltis|first5=Douglas E.|date=2018|title=Plastid phylogenomic analysis of green plants: A billion years of evolutionary history|url=https://doi.org/10.1002/ajb2.1048|journal=American Journal of Botany|language=en|volume=105|issue=3|pages=291–301|doi=10.1002/ajb2.1048|issn=0002-9122|via=}}</ref> Those which have been called "plants" are in bold.{{barlabel|size=6|at=3|label=groups traditionally<br />included in the "algae"|cladogram={{cladex
|label1='''Archaeplastida'''
|1={{cladex
|1=[[Rhodophyta]] (red algae)|bar1=darkgreen|barbegin1=darkgreen
|2={{cladex
|1=[[Glaucophyta]] (glaucophyte algae)|bar1=darkgreen
|label2='''Green plants'''/[[Green algae]]
|2={{cladex
|1={{cladex
|1=[[Mesostigmatophyceae]]|bar1=darkgreen
|2={{cladex
|1=[[Chlorokybophyceae]]|bar1=darkgreen
|2=[[Spirotaenia]]|bar2=darkgreen}}
}}
|2={{cladex
|1=[[Chlorophyta]]|bar1=darkgreen
|label2=[[Streptophyta]]
|2={{cladex
|1=
|state1=double|bar1=darkgreen
|2={{cladex
|1=[[Charales]] (stoneworts)|bar1=darkgreen
|2={{cladex
|state1=double
|1= |barend1=darkgreen
|2='''land plants''' or [[embryophyte]]s
}}
}}
}}
}}
}}
}}
}}
}}}}The way in which the groups of green algae are combined and named varies considerably between authors.
=== Algae ===
[[File:Haeckel Siphoneae.jpg|thumb|[[Green algae]] from [[Ernst Haeckel]]'s ''[[Kunstformen der Natur]]'', 1904.]]
{{Main|Algae}}
Algae comprise several different groups of organisms which produce food by photosynthesis and thus have traditionally been included in the plant kingdom. The [[seaweed]]s range from large multicellular algae to single-celled organisms and are classified into three groups, the [[brown algae|brown]], [[red algae|red]] and [[green algae]]. There is good evidence that the brown algae evolved independently from the others, from non-photosynthetic ancestors that formed endosymbiotic relationships with red algae rather than from cyanobacteria, and they are no longer classified as plants as defined here.<ref>{{cite journal |last=Margulis |first=L. |year=1974 |title=Five-kingdom classification and the origin and evolution of cells |journal=Evolutionary Biology |volume=7 |pages=45–78 |doi=10.1007/978-1-4615-6944-2_2}}</ref><ref name="Raven 2005" />
The Viridiplantae, the green plants – green algae and land plants – form a [[clade]], a group consisting of all the descendants of a common ancestor. With a few exceptions, the green plants have the following features in common; primary [[chloroplast]]s derived from cyanobacteria containing [[chlorophyll]]s ''a'' and ''b'', cell walls containing [[cellulose]], and food stores in the form of [[starch]] contained within the plastids. They undergo closed [[mitosis]] without [[centriole]]s, and typically have [[mitochondrion|mitochondria]] with flat cristae. The [[chloroplast]]s of green plants are surrounded by two membranes, suggesting they originated directly from endosymbiotic [[cyanobacteria]].
Two additional groups, the [[Rhodophyta]] (red algae) and [[Glaucophyta]] (glaucophyte algae), also have primary chloroplasts that appear to be derived directly from endosymbiotic [[cyanobacteria]], although they differ from Viridiplantae in the pigments which are used in photosynthesis and so are different in colour. These groups also differ from green plants in that the storage polysaccharide is [[floridean starch]] and is stored in the cytoplasm rather than in the plastids. They appear to have had a common origin with Viridiplantae and the three groups form the clade [[Archaeplastida]], whose name implies that their chloroplasts were derived from a single ancient endosymbiotic event. This is the broadest modern definition of the term 'plant'.
In contrast, most other algae (e.g. [[heterokont|brown algae/diatoms]], [[haptophyte]]s, [[dinoflagellate]]s, and [[euglenid]]s) not only have different pigments but also have chloroplasts with three or four surrounding membranes. They are not close relatives of the Archaeplastida, presumably having acquired chloroplasts separately from ingested or symbiotic green and red algae. They are thus not included in even the broadest modern definition of the plant kingdom, although they were in the past.
The green plants or Viridiplantae were traditionally divided into the green algae (including the stoneworts) and the land plants. However, it is now known that the land plants evolved from within a group of green algae, so that the green algae by themselves are a [[paraphyly|paraphyletic]] group, i.e. a group that excludes some of the descendants of a common ancestor. Paraphyletic groups are generally avoided in modern classifications, so that in recent treatments the Viridiplantae have been divided into two clades, the [[Chlorophyta]] and the [[Streptophyta]] (including the land plants and Charophyta).<ref name="LewisMcCourt2004">{{Citation |last=Lewis |first=Louise A. |last2=McCourt |first2=R.M. |year=2004 |title=Green algae and the origin of land plants |journal=Am. J. Bot. |volume=91 |issue=10 |pages=1535–1556 |doi=10.3732/ajb.91.10.1535 |lastauthoramp=yes |pmid=21652308}}</ref><ref name="BeckerMarin2009">{{Citation |last=Becker |first=B. |last2=Marin |first2=B. |year=2009 |title=Streptophyte algae and the origin of embryophytes |journal=Annals of Botany |volume=103 |issue=7 |pages=999–1004 |doi=10.1093/aob/mcp044 |lastauthoramp=yes |pmid=19273476 |pmc=2707909}}</ref>
The Chlorophyta (a name that has also been used for ''all'' green algae) are the sister group to the Charophytes, from which the land plants evolved. There are about 4,300 species,<ref name="Algaebase">{{cite web |url= http://www.algaebase.org/browse/taxonomy/?id=4307 |publisher= ''AlgaeBase version 4.2'' World-wide electronic publication, National University of Ireland, Galway |accessdate= 2007-09-23 |title= Phylum: Chlorophyta taxonomy browser |author1=Guiry, M.D. |author2=Guiry, G.M. |lastauthoramp=yes |year= 2007 }}</ref> mainly unicellular or multicellular marine organisms such as the sea lettuce, ''[[Ulva (genus)|Ulva]]''.
The other group within the Viridiplantae are the mainly freshwater or terrestrial Streptophyta, which consists of the land plants together with the Charophyta, itself consisting of several groups of green algae such as the [[desmid]]s and [[Charales|stoneworts]]. Streptophyte algae are either unicellular or form multicellular filaments, branched or unbranched.<ref name="BeckerMarin2009" /> The genus ''[[Spirogyra]]'' is a filamentous streptophyte alga familiar to many, as it is often used in teaching and is one of the organisms responsible for the algal "scum" on ponds. The freshwater stoneworts strongly resemble land plants and are believed to be their closest relatives.{{citation needed|date=March 2017}} Growing immersed in fresh water, they consist of a central stalk with whorls of branchlets.
=== Fungi ===
{{Main|Fungi}}
[[Carl Linnaeus|Linnaeus']] original classification placed the fungi within the Plantae, since they were unquestionably neither animals or minerals and these were the only other alternatives. With 19th century developments in [[microbiology]], [[Ernst Haeckel]] introduced the new kingdom Protista in addition to Plantae and Animalia, but whether fungi were best placed in the Plantae or should be reclassified as protists remained controversial. In 1969, [[Robert Whittaker]] proposed the creation of the kingdom Fungi. Molecular evidence has since shown that the [[most recent common ancestor]] (concestor), of the Fungi was probably more similar to that of the Animalia than to that of Plantae or any other kingdom.<ref>{{cite book |author=Deacon, J.W. |year=2005 |title=Fungal Biology |publisher=Wiley |isbn=978-1-4051-3066-0 |url=https://books.google.com/books?id=FMSn4RIoGGoC }}</ref>
Whittaker's original reclassification was based on the fundamental difference in nutrition between the Fungi and the Plantae. Unlike plants, which generally gain carbon through photosynthesis, and so are called [[autotroph]]s, fungi do not possess chloroplasts and generally obtain carbon by breaking down and absorbing surrounding materials, and so are called [[heterotroph]]ic [[saprotrophs]]. In addition, the substructure of multicellular fungi is different from that of plants, taking the form of many chitinous microscopic strands called [[hypha]]e, which may be further subdivided into cells or may form a [[syncytium]] containing many [[eukaryotic]] [[cell nucleus|nuclei]]. Fruiting bodies, of which [[mushroom]]s are the most familiar example, are the reproductive structures of fungi, and are unlike any structures produced by plants.
== Diversity ==
The table below shows some species count estimates of different green plant (Viridiplantae) divisions. It suggests there are about 300,000 species of living Viridiplantae, of which 85–90% are flowering plants. (Note: as these are from different sources and different dates, they are not necessarily comparable, and like all species counts, are subject to a degree of uncertainty in some cases.)
{| class="wikitable" style="float:left; margin-left:1em;"
|+'''Diversity of living green plant (Viridiplantae) divisions'''
|-
! style="background:lightgreen; text-align:center;"| Informal group
! style="background:lightgreen; text-align:center;"| Division name
! style="background:lightgreen; text-align:center;"| Common name
! style="background:lightgreen; text-align:center;"| No. of living species
! style="background:lightgreen; text-align:center;"| Approximate No. in informal group
|-
| rowspan="2" style="background:lightgrey; vertical-align:top;"| [[Green algae]]
| '''[[Chlorophyta]]'''
| style="text-align:left;"| [[green algae]] (chlorophytes)
| style="text-align:right;"| 3,800–4,300 <ref>Van den Hoek, C., D. G. Mann, & H. M. Jahns, 1995. ''Algae: An Introduction to Phycology''. pages 343, 350, 392, 413, 425, 439, & 448 (Cambridge: Cambridge University Press). {{ISBN|0-521-30419-9}}</ref><ref name=AlgaeBase_Chlorophyta>{{Citation |last=Guiry |first=M.D. |last2=Guiry |first2=G.M. |year=2011 |title=AlgaeBase : Chlorophyta |publisher=World-wide electronic publication, National University of Ireland, Galway |url=http://www.algaebase.org/browse/taxonomy/?searching=true&gettaxon=Chlorophyta |accessdate=2011-07-26 |lastauthoramp=yes }}</ref>
| rowspan="2" style="text-align:right; vertical-align:top;"| 8,500
(6,600–10,300)
|-
| '''[[Charophyta]]'''
| style="text-align:left;"| [[green algae]] (e.g. [[desmid]]s & [[stonewort]]s)
| style="text-align:right;"| 2,800–6,000 <ref name=AlgaeBase_Charophyta>{{Citation |last=Guiry |first=M.D. |last2=Guiry |first2=G.M. |year=2011 |title=AlgaeBase : Charophyta |publisher=World-wide electronic publication, National University of Ireland, Galway |url=http://www.algaebase.org/browse/taxonomy/?searching=true&gettaxon=Charophyta |accessdate=2011-07-26 |lastauthoramp=yes }}</ref><ref>Van den Hoek, C., D. G. Mann, & H. M. Jahns, 1995. ''Algae: An Introduction to Phycology''. pages 457, 463, & 476. (Cambridge: Cambridge University Press). {{ISBN|0-521-30419-9}}</ref>
|-
| rowspan="3" style="background:lightgrey; vertical-align:top;"| [[Bryophyte]]s
| '''[[Marchantiophyta]]'''
| style="text-align:left;"| liverworts
| style="text-align:right;"| 6,000–8,000 <ref>Crandall-Stotler, Barbara. & Stotler, Raymond E., 2000. "Morphology and classification of the Marchantiophyta". page 21 ''in'' A. Jonathan Shaw & Bernard Goffinet (Eds.), ''Bryophyte Biology''. (Cambridge: Cambridge University Press). {{ISBN|0-521-66097-1}}</ref>
| rowspan="3" style="text-align:right; vertical-align:top;"| 19,000
(18,100–20,200)
|-
| '''[[Anthocerotophyta]]'''
| style="text-align:left;"| hornworts
| style="text-align:right;"| 100–200 <ref>Schuster, Rudolf M., ''The Hepaticae and Anthocerotae of North America'', volume VI, pages 712–713. (Chicago: Field Museum of Natural History, 1992). {{ISBN|0-914868-21-7}}.</ref>
|-
| '''[[Moss|Bryophyta]]'''
| style="text-align:left;"| mosses
| style="text-align:right;"| 12,000 <ref name="Goffinet & Buck 2004">{{cite journal |last=Goffinet |first= Bernard |author2=William R. Buck |year=2004 |title=Systematics of the Bryophyta (Mosses): From molecules to a revised classification |journal=Monographs in Systematic Botany |volume=98 |pages=205–239 |publisher= Missouri Botanical Garden Press }}</ref>
|-
| rowspan="2" style="background:lightgrey; vertical-align:top;"| [[Pteridophyte]]s
| '''[[Lycopodiophyta]]'''
| style="text-align:left;"| club mosses
| style="text-align:right;"| 1,200 <ref name="Raven 2005">{{cite book |last=Raven |first=Peter H. |first2=Ray F. |last2=Evert |first3=Susan E. |last3=Eichhorn |year=2005 |title=Biology of Plants |edition=7th |location=New York |publisher=W. H. Freeman and Company |isbn=0-7167-1007-2 }}</ref>
| rowspan="2" style="text-align:right; vertical-align:top;"| 12,000
(12,200)
|-
| '''[[Fern|Pteridophyta]]'''
| style="text-align:left;"| ferns, whisk ferns & horsetails
| style="text-align:right;"| 11,000 <ref name="Raven 2005" />
|-
| rowspan="5" style="background:lightgrey; vertical-align:top;"| [[Seed plant]]s
| '''[[Cycad]]ophyta'''
| style="text-align:left;"| cycads
| style="text-align:right;"| 160 <ref>{{cite book |last=Gifford |first=Ernest M. |first2=Adriance S. |last2=Foster |year=1988 |title=Morphology and Evolution of Vascular Plants |edition=3rd |page=358 |location=New York |publisher=W. H. Freeman and Company |isbn=0-7167-1946-0 }}</ref>
| rowspan="5" style="text-align:right; vertical-align:top;"| 260,000
(259,511)
|-
| '''[[Ginkgophyta]]'''
| style="text-align:left;"| ginkgo
| style="text-align:right;"| 1 <ref>{{cite book |last=Taylor |first=Thomas N. |first2=Edith L. |last2=Taylor |year=1993 |title=The Biology and Evolution of Fossil Plants |page=636 |location=New Jersey |publisher=Prentice-Hall |isbn=0-13-651589-4 }}</ref>
|-
| '''[[Pinophyta]]'''
| style="text-align:left;"| conifers
| style="text-align:right;"| 630 <ref name="Raven 2005" />
|-
| '''[[Gnetophyta]]'''
| style="text-align:left;"| gnetophytes
| style="text-align:right;"| 70 <ref name="Raven 2005" />
|-
| '''[[Flowering plant|Magnoliophyta]]'''
| style="text-align:left;"| flowering plants
| style="text-align:right;"| 258,650 <ref>International Union for Conservation of Nature and Natural Resources, 2006. ''[http://www.iucnredlist.org/ IUCN Red List of Threatened Species:Summary Statistics]''</ref>
|}
{{Clear}}
The naming of plants is governed by the [[International Code of Nomenclature for algae, fungi, and plants]] and [[International Code of Nomenclature for Cultivated Plants]] (see [[cultivated plant taxonomy]]).
=== Evolution ===
{{Life timeline}}
{{further|Evolutionary history of plants}}
The evolution of plants has resulted in increasing [[Evolutionary grade|levels of complexity]], from the earliest [[algal mat]]s, through [[bryophyte]]s, [[lycopod]]s, [[fern]]s to the complex [[gymnosperm]]s and [[angiosperm]]s of today. Plants in all of these groups continue to thrive, especially in the environments in which they evolved.
An algal scum formed on the land {{Ma|1200}}, but it was not until the [[Ordovician Period]], around {{Ma|450}}, that land plants appeared.<ref>"The oldest fossils reveal evolution of non-vascular plants by the middle to late Ordovician Period (≈450–440 m.y.a.) on the basis of fossil spores" [http://www.clas.ufl.edu/users/pciesiel/gly3150/plant.html Transition of plants to land] {{webarchive|url=https://web.archive.org/web/20080302040410/http://www.clas.ufl.edu/users/pciesiel/gly3150/plant.html |date=2 March 2008 }}</ref> However, new evidence from the study of carbon isotope ratios in Precambrian rocks has suggested that complex photosynthetic plants developed on the earth over 1000 m.y.a.<ref>{{Cite journal|last=Strother|first=Paul K.|last2=Battison|first2=Leila|last3=Brasier|first3=Martin D.|last4=Wellman|first4=Charles H.|date=26 May 2011|title=Earth's earliest non-marine eukaryotes|url=https://www.nature.com/articles/nature09943|journal=[[Nature (journal)|Nature]]|volume=473|pages=505–509|doi=10.1038/nature09943|via=|bibcode=2011Natur.473..505S}}</ref> For more than a century it has been assumed that the ancestors of land plants evolved in aquatic environments and then adapted to a life on land, an idea usually credited to botanist [[Frederick Orpen Bower]] in his 1908 book "The Origin of a Land Flora". A recent alternative view, supported by genetic evidence, is that they evolved from terrestrial single-celled algae.<ref>{{Cite journal|last=Harholt|first=Jesper|last2=Moestrup|first2=Øjvind|last3=Ulvskov|first3=Peter|date=2016-02-01|title=Why Plants Were Terrestrial from the Beginning|url=http://www.cell.com/trends/plant-science/abstract/S1360-1385(15)00300-3|journal=[[Trends (journals)|Trends in Plant Science]]|language=English|publisher=[[Cell Press]]|volume=21|issue=2|pages=96–101|doi=10.1016/j.tplants.2015.11.010|issn=1360-1385|pmid=26706443|via=}}</ref> Primitive land plants began to diversify in the late [[Silurian Period]], around {{Ma|420}}, and the results of their diversification are displayed in remarkable detail in an early [[Devonian]] fossil assemblage from the [[Rhynie chert]]. This chert preserved early plants in cellular detail, petrified in volcanic springs. By the middle of the Devonian Period most of the features recognised in plants today are present, including roots, leaves and secondary wood, and by late Devonian times seeds had evolved.<ref name="Rothwelletal989">{{cite journal |last1= Rothwell |first1= G. W. |last2= Scheckler |first2= S. E. |last3= Gillespie |first3= W. H. |year= 1989 |title= ''Elkinsia'' gen. nov., a Late Devonian gymnosperm with cupulate ovules |journal= Botanical Gazette |volume= 150 |issue= 2 |pages= 170–189 |doi= 10.1086/337763 |publisher= University of Chicago Press |jstor=2995234}}</ref> Late Devonian plants had thereby reached a degree of sophistication that allowed them to form forests of tall trees. Evolutionary innovation continued in the Carboniferous and later geological periods and is ongoing today. Most plant groups were relatively unscathed by the [[Permo-Triassic extinction event]], although the structures of communities changed. This may have set the scene for the evolution of flowering plants in the Triassic (~{{ma|200}}), which exploded in the Cretaceous and Tertiary. The latest major group of plants to evolve were the grasses, which became important in the mid Tertiary, from around {{Ma|40}}. The grasses, as well as many other groups, evolved new mechanisms of metabolism to survive the low {{co2}} and warm, dry conditions of the tropics over the last {{Ma|10|million years}}.
A 1997 proposed [[phylogenetic tree]] of Plantae, after Kenrick and Crane,<ref>Kenrick, Paul & Peter R. Crane. 1997. ''The Origin and Early Diversification of Land Plants: A Cladistic Study.'' (Washington, D.C., Smithsonian Institution Press.) {{ISBN|1-56098-730-8}}.</ref> is as follows, with modification to the Pteridophyta from Smith ''et al.''<ref>{{cite journal|author1=Smith Alan R. |author2=Pryer Kathleen M. |author3=Schuettpelz E. |author4=Korall P. |author5=Schneider H. |author6=Wolf Paul G. |title=A classification for extant ferns |year=2006 |journal=Taxon |volume=55 |issue=3 |pages=705–731 |url=http://www.pryerlab.net/publication/fichier749.pdf |format=PDF |doi=10.2307/25065646 |deadurl=yes |archiveurl=https://web.archive.org/web/20080226232147/http://www.pryerlab.net/publication/fichier749.pdf |archivedate=26 February 2008 |df= }}</ref> The [[Prasinophyceae]] are a [[paraphyletic]] assemblage of early diverging green algal lineages, but are treated as a group outside the Chlorophyta:<ref name="leliaert" /> later authors have not followed this suggestion.
{{clade| style=font-size:75%;line-height:75%;
|1={{clade
|1=[[Prasinophyceae]] (micromonads)
|2={{clade
|label1=Streptobionta
|1={{clade
|1={{clade
|label1=[[Embryophyte]]s
|1={{clade
|1={{clade
|label1=Stomatophytes
|1={{clade
|1={{clade
|label1=[[Polysporangiophyte|Polysporangiates]]
|1={{clade
|1={{clade
|label1=[[Vascular plant|Tracheophytes]]
|1={{clade
|label1=Eutracheophytes
|1={{clade
|label1=Euphyllophytina
|1={{clade
|label1=Lignophyta
|1={{clade
|1='''[[Spermatophyte]]s''' (seed plants)
|2=[[Progymnospermophyta]] †
}}
|label2='''[[Fern|Pteridophyta]]'''
|2={{clade
|1={{clade
|1=[[Pteridopsida]] (true ferns)
|2=[[Marattiopsida]]
|3=[[Equisetopsida]] (horsetails)
|4=[[Psilotopsida]] (whisk ferns & adders'-tongues)
|5=[[Cladoxylopsid]]a †
}}
}}
}}
|label2=Lycophytina
|2={{clade
|1='''[[Lycopodiophyta]]'''
|2=[[Zosterophyllophyta]] †
}}
}}
|2=[[Rhyniophyta]] †
}}
}}
|2=''[[Aglaophyton]]'' †
|3=[[Horneophytopsida]] †
}}
}}
|2='''[[Moss|Bryophyta]]''' (mosses)
|3='''[[Anthocerotophyta]]''' (hornworts)
}}
}}
|2='''[[Marchantiophyta]]''' (liverworts)
}}
}}
|2='''[[Charophyta]]'''
}}
}}
|3={{clade
|label1='''[[Chlorophyta]]'''
|1={{clade
|1={{clade
|1=[[Trebouxiophyceae]] (Pleurastrophyceae)
|2=[[Chlorophyceae]]
}}
|2=[[Ulvophyceae]]
}}
}}
}}
}}
A newer proposed classification follows Leliaert et al. 2011<ref name="LeliaertVerbruggen2011">{{cite journal|last1=Leliaert|first1=Frederik|last2=Verbruggen|first2=Heroen|last3=Zechman|first3=Frederick W.|title=Into the deep: New discoveries at the base of the green plant phylogeny|journal=BioEssays|volume=33 |issue=9 |year=2011 |pages=683–692 |issn=0265-9247 |doi=10.1002/bies.201100035 |pmid=21744372}}</ref> and modified with Silar 2016<ref>{{citation | date=2016| author = Silar, Philippe| title = Protistes Eucaryotes: Origine, Evolution et Biologie des Microbes Eucaryotes| url=https://hal.archives-ouvertes.fr/hal-01263138| volume= |issue= |pages=1–462 |journal=HAL archives-ouvertes | doi=}}</ref><ref name="Sánchez-Baracaldo E7737–E7745"/> for the green algae clades and Novíkov & Barabaš-Krasni 2015<ref>{{cite journal | author=Novíkov & Barabaš-Krasni | year=2015 | title=Modern plant systematics | journal= | volume=| issue= | page=685 | publisher=Liga-Pres| isbn=978-966-397-276-3 |doi=10.13140/RG.2.1.4745.6164}}</ref> for the land plants clade. Notice that the Prasinophyceae are here placed inside the Chlorophyta.
{{barlabel |size=1 |at=0.1 |label=[[Green algae]]|cladogram=
{{clade| style=font-size:90%;line-height:80%;
|label1=[[Viridiplantae]]
|1={{cladex
|1= {{cladex
|barbegin1=darkgreen
|1=[[Chlorokybophyceae|Chlorokybophyta]]
|2=[[Mesostigmatophyceae|Mesostigmatophyta]] |bar2=darkgreen
}}
|2={{cladex
|label1=Chlorobionta
|1=[[Chlorophyta]] |bar1=darkgreen
|label2=[[Streptophyta|Streptobionta]]
|2={{cladex
|1=[[Klebsormidiophyceae|Klebsormidiophyta]] |bar1=darkgreen
|label2=[[Phragmoplastophyta]]
|2={{cladex
|1=[[Charophyta]] <small>Rabenhorst 1863 emend. Lewis & McCourt 2004</small> (Stoneworts)|bar1=darkgreen
|2={{cladex
|1=[[Chaetosphaeridiales]] <small>Marin & Melkonian 1999</small> |bar1=darkgreen
|2=[[Coleochaetophyceae|Coleochaetophyta]] |bar2=darkgreen
|3={{cladex
|1=[[Zygnematophyceae|Zygnematophyta]]|barend1=darkgreen
|label2=[[Embryophyta|Embryobiotes]]
|2={{cladex
|1=[[Marchantiophyta]] (Liverworts)
|label2=[[Stomatophyta]]
|2={{cladex
|1=[[Moss|Bryophyta]] (True mosses)
|2={{cladex
|1=[[Anthocerotophyta]] (Non-flowering hornworts)
|label2=[[Polysporangiophyta]]
|2={{cladex
|1=[[Horneophytopsida|Horneophyta]]
|2={{cladex
|1=[[Aglaophyton|Aglaophyta]]
|2=[[Tracheophyta]] (Vascular Plants)
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}
}}
=== Embryophytes ===
{{Main|Embryophyte}}
[[File:Ferns02.jpg|thumb|''[[Dicksonia antarctica]]'', a species of [[tree fern]]]]
The plants that are likely most familiar to us are the [[multicellular]] land plants, called [[embryophyte]]s. Embryophytes include the [[vascular plant]]s, such as ferns, conifers and flowering plants. They also include the ''[[bryophyte]]s'', of which [[moss]]es and [[Marchantiophyta|liverworts]] are the most common.
All of these plants have [[eukaryote|eukaryotic]] cells with [[cell wall]]s composed of [[cellulose]], and most obtain their energy through [[photosynthesis]], using [[light]], water and [[carbon dioxide]] to synthesize food. About three hundred plant species do not photosynthesize but are [[parasite]]s on other species of photosynthetic plants. Embryophytes are distinguished from [[green algae]], which represent a mode of photosynthetic life similar to the kind modern plants are believed to have evolved from, by having specialized reproductive organs protected by non-reproductive tissues.
Bryophytes first appeared during the early [[Paleozoic]]. They are mainly live in habitats where moisture is available for significant periods, although some species, such as [[Targionia (plant)|''Targionia'']] are desiccation-tolerant. Most species of bryophytes remain small throughout their life-cycle. This involves an alternation between two generations: a [[haploid]] stage, called the [[gametophyte]], and a [[diploid]] stage, called the [[sporophyte]]. In bryophytes, the sporophyte is always unbranched and remains nutritionally dependent on its parent gametophyte. The embryophytes have the ability to secrete a [[Plant cuticle|cuticle]] on their outer surface, a waxy layer that confers resistant to desiccation. In the [[moss]]es and [[hornwort]]s a cuticle is usually only produced on the sporophyte. [[Stomata]] are absent from liverworts, but occur on the sporangia of mosses and hornworts, allowing gas exchange.
Vascular plants first appeared during the [[Silurian]] period, and by the [[Devonian]] had diversified and spread into many different terrestrial environments. They developed a number of adaptations that allowed them to spread into increasingly more arid places, notably the vascular tissues [[xylem]] and [[phloem]], that transport water and food throughout the organism. Root systems capable of obtaining soil water and nutrients also evolved during the Devonian. In modern vascular plants, the sporophyte is typically large, branched, nutritionally independent and long-lived, but there is increasing evidence that Paleozoic gametophytes were just as complex as the sporophytes. The gametophytes of all vascular plant groups evolved to become reduced in size and prominence in the life cycle.
In seed plants, the [[gametophyte#Heteromorphy|microgametophyte]] is reduced from a multicellular free-living organism to a few cells in a pollen grain and the miniaturised [[gametophyte#Heteromorphy|megagametophyte]] remains inside the megasporangium, attached to and dependent on the parent plant. A megasporangium enclosed in a protective layer called an integument is known as an [[ovule]]. After fertilisation by means of sperm produced by [[pollen]] grains, an embryo sporophyte develops inside the ovule. The integument becomes a seed coat, and the ovule develops into a seed. Seed plants can survive and reproduce in extremely arid conditions, because they are not dependent on free water for the movement of sperm, or the development of free living gametophytes.
The first seed plants, [[Pteridospermatophyta|pteridosperms]] (seed ferns), now extinct, appeared in the Devonian and diversified through the Carboniferous. They were the ancestors of modern [[gymnosperm]]s, of which four surviving groups are widespread today, particularly the [[conifer]]s, which are dominant [[tree]]s in several [[biome]]s. The name gymnosperm comes from the [[Greek language|Greek]] composite word ''γυμνόσπερμος'' (γυμνός gymnos, "naked" and σπέρμα sperma, "seed"), as the ovules and subsequent seeds are not enclosed in a protective structure (carpels or fruit), but are borne naked, typically on cone scales.
=== Fossils ===
{{Main|Paleobotany|Evolutionary history of plants}}
[[File:Petrified forest log 1 md.jpg|thumb|upright|A petrified log in [[Petrified Forest National Park]], Arizona]]
Plant [[fossil]]s include roots, wood, leaves, seeds, fruit, [[pollen]], [[spore]]s, [[phytolith]]s, and [[amber]] (the fossilized resin produced by some plants). Fossil land plants are recorded in terrestrial, lacustrine, fluvial and nearshore marine sediments. [[Pollen]], [[spores]] and algae ([[dinoflagellate]]s and [[acritarch]]s) are used for dating sedimentary rock sequences. The remains of fossil plants are not as common as fossil animals, although plant fossils are locally abundant in many regions worldwide.
The earliest fossils clearly assignable to Kingdom Plantae are fossil green algae from the [[Cambrian]]. These fossils resemble [[Calcification|calcified]] [[multicellular]] members of the [[Dasycladales]]. Earlier [[Precambrian]] fossils are known that resemble single-cell green algae, but definitive identity with that group of algae is uncertain.
The earliest fossils attributed to green algae date from the [[Precambrian]] (ca. 1200 mya).<ref>{{cite book |last=Knoll |first=Andrew H |title=Life on a Young Planet: The First Three Billion Years of Evolution on Earth |publisher=Princeton University Press |year=2003 }}</ref><ref>{{cite book |last=Tappan |first=H |title=Palaeobiology of Plant Protists |publisher=Freeman, San Francisco |year=1980 }}</ref> The resistant outer walls of [[Prasinophyceae|prasinophyte]] cysts (known as phycomata) are well preserved in fossil deposits of the [[Paleozoic]] (ca. 250-540 mya). A filamentous fossil (''Proterocladus'') from middle Neoproterozoic deposits (ca. 750 mya) has been attributed to the [[Cladophorales]], while the oldest reliable records of the [[Bryopsidales]], [[Dasycladales]]) and [[Charales|stoneworts]] are from the [[Paleozoic]].<ref name="leliaert">{{cite journal|author=Leliaert, F., Smith, D.R., Moreau, H., Herron, M.D., Verbruggen, H., Delwiche, C.F. & De Clerck, O. |year=2012 |title=Phylogeny and molecular evolution of the green algae |url=http://images.algaebase.org/pdf/5628E58F0ecc431F0CsJm2B04CAD/49951.pdf |doi=10.1080/07352689.2011.615705 |journal=Critical Reviews in Plant Sciences |volume=31 |pages=1–46 |format=PDF |deadurl=yes |archiveurl=https://web.archive.org/web/20150626102452/http://images.algaebase.org/pdf/5628E58F0ecc431F0CsJm2B04CAD/49951.pdf |archivedate=26 June 2015 |df= }}</ref><ref name="ButterfieldKnoll1994">{{cite journal |last1=Butterfield |first1=Nicholas J.|last2=Knoll|first2=Andrew H.|last3=Swett |first3=Keene |title=Paleobiology of the Neoproterozoic Svanbergfjellet Formation, Spitsbergen |journal=Lethaia |volume=27 |issue=1 |year=1994 |pages=76–76|issn=0024-1164 |doi=10.1111/j.1502-3931.1994.tb01558.x}}</ref>
The oldest known fossils of embryophytes date from the [[Ordovician]], though such fossils are fragmentary. By the [[Silurian]], fossils of whole plants are preserved, including the simple vascular plant ''[[Cooksonia]]'' in mid-Silurian and the much larger and more complex [[lycophyte]] ''[[Baragwanathia longifolia]]'' in late Silurian. From the early Devonian [[Rhynie chert]], detailed fossils of lycophytes and [[rhyniophyte]]s have been found that show details of the individual cells within the plant organs and the symbiotic association of these plants with fungi of the order [[Glomerales|Glomales]]. The [[Devonian period]] also saw the evolution of leaves and roots, and the first modern tree, ''[[Archaeopteris]]''. This tree with fern-like foliage and a trunk with conifer-like wood was [[heterosporous]] producing spores of two different sizes, an early step in the evolution of seeds.<ref name=Stewart>{{cite book|first1=Wilson A. |last1=Stewart|first2=Gar W.|last2=Rothwell|title=Paleobotany and the evolution of plants|edition=2|date=1993|publisher=Cambridge University Press|isbn=0521382947 }}</ref>
The [[Coal measure]]s are a major source of [[Paleozoic]] plant fossils, with many groups of plants in existence at this time. The spoil heaps of coal mines are the best places to collect; [[coal]] itself is the remains of fossilised plants, though structural detail of the plant fossils is rarely visible in coal. In the [[Fossil Grove]] at [[Victoria Park, Glasgow|Victoria Park]] in [[Glasgow]], Scotland, the stumps of ''[[Lepidodendron]]'' trees are found in their original growth positions.
The fossilized remains of [[conifer]] and [[angiosperm]] [[root]]s, [[plant stem|stems]] and [[branch]]es may be locally abundant in lake and inshore [[sedimentary rock]]s from the [[Mesozoic]] and [[Cenozoic]] eras. [[Coast Redwood|Sequoia]] and its allies, [[magnolia]], [[oak]], and [[Arecaceae|palms]] are often found.
[[Petrified wood]] is common in some parts of the world, and is most frequently found in arid or desert areas where it is more readily exposed by [[erosion]]. Petrified wood is often heavily [[silicified]] (the [[organic material]] replaced by [[silicon dioxide]]), and the impregnated tissue is often preserved in fine detail. Such specimens may be cut and polished using [[lapidary]] equipment. Fossil forests of petrified wood have been found in all continents.
Fossils of seed ferns such as ''[[Glossopteris]]'' are widely distributed throughout several continents of the [[Southern Hemisphere]], a fact that gave support to [[Alfred Wegener]]'s early ideas regarding [[Continental drift]] theory.
== Structure, growth and development ==
{{further|Plant morphology}}
[[File:Leaf 1 web.jpg|thumb|The [[leaf]] is usually the primary site of [[photosynthesis]] in plants.]]
Most of the solid material in a plant is taken from the atmosphere. Through the process of [[photosynthesis]], most plants use the energy in [[sunlight]] to convert [[carbon dioxide]] from the atmosphere, plus [[water]], into simple [[sugar]]s. These sugars are then used as building blocks and form the main structural component of the plant. [[Chlorophyll]], a green-colored, [[magnesium]]-containing [[pigment]] is essential to this process; it is generally present in plant [[leaf|leaves]], and often in other plant parts as well. [[Parasitic plant]]s, on the other hand, use the resources of their host to provide the materials needed for metabolism and growth.
Plants usually rely on soil primarily for support and water (in quantitative terms), but they also obtain [[chemical compound|compounds]] of [[nitrogen]], [[phosphorus]], [[potassium]], magnesium and other elemental [[nutrient]]s from the soil. [[Epiphyte|Epiphytic]] and [[lithophyte|lithophytic]] plants depend on air and nearby debris for nutrients, and [[carnivorous plant]]s supplement their nutrient requirements, particularly for nitrogen and phosphorus, with insect prey that they capture. For the majority of plants to grow successfully they also require [[oxygen]] in the atmosphere and around their roots ([[soil gas]]) for [[Cellular respiration|respiration]]. Plants use oxygen and [[glucose]] (which may be produced from stored [[starch]]) to provide energy.<ref>{{cite book|title=Life on Earth|year=1973|isbn=0-87893-934-2|page=145|author=[[Edward O. Wilson]]|edition=First|display-authors=etal}}</ref> Some plants grow as submerged aquatics, using oxygen dissolved in the surrounding water, and a few specialized vascular plants, such as [[mangrove]]s and reed (''[[Phragmites australis]]''),<ref name=Crawford>{{cite journal|first=Crawford|last=R.M.M.|date=1982|title=Physiological responses in flooding|journal=Encyclopedia of Plant Physiology|volume=12B|pages=453–477|publisher=Springer Verlag|location=Berlin}}</ref> can grow with their roots in [[anoxic waters|anoxic]] conditions.
=== Factors affecting growth ===
The genome of a plant controls its growth. For example, selected varieties or genotypes of wheat grow rapidly, maturing within 110 days, whereas others, in the same environmental conditions, grow more slowly and mature within 155 days.<ref name=Robbins>Robbins, W.W., Weier, T.E., ''et al.'', ''Botany:Plant Science'', 3rd edition, Wiley International, New York, 1965.</ref>
Growth is also determined by environmental factors, such as [[temperature]], available [[water]], available [[light]], [[carbon dioxide]] and available [[nutrient]]s in the soil. Any change in the availability of these external conditions will be reflected in the plant's growth and the timing of its development.
Biotic factors also affect plant growth. Plants can be so crowded that no single individual produces normal growth, causing [[etiolation]] and [[chlorosis]]. Optimal plant growth can be hampered by grazing animals, suboptimal soil composition, lack of [[mycorrhiza]]l fungi, and attacks by insects or [[plant pathology|plant diseases]], including those caused by bacteria, fungi, viruses, and nematodes.<ref name=Robbins />
[[File:Eenbruinigherfstblad.jpg|thumb|left|There is no photosynthesis in deciduous leaves in autumn.]]
Simple plants like algae may have short life spans as individuals, but their populations are commonly seasonal. [[Annual plant]]s grow and reproduce within one [[growing season]], [[biennial plant]]s grow for two growing seasons and usually reproduce in second year, and [[perennial plant]]s live for many growing seasons and once mature will often reproduce annually. These designations often depend on climate and other environmental factors. Plants that are annual in [[alpine climate|alpine]] or [[temperate]] regions can be biennial or perennial in warmer climates. Among the vascular plants, perennials include both [[evergreen]]s that keep their leaves the entire year, and [[deciduous]] plants that lose their leaves for some part of it. In temperate and [[boreal climate]]s, they generally lose their leaves during the winter; many [[tropical]] plants lose their leaves during the [[dry season]].
The growth rate of plants is extremely variable. Some mosses grow less than 0.001 millimeters per hour (mm/h), while most trees grow 0.025-0.250 mm/h. Some climbing species, such as [[kudzu]], which do not need to produce thick supportive tissue, may grow up to 12.5 mm/h.
Plants protect themselves from [[frost]] and [[dehydration]] stress with [[antifreeze protein]]s, [[Heat shock protein|heat-shock proteins]] and sugars ([[sucrose]] is common). LEA ([[Late Embryogenesis Abundant proteins|Late Embryogenesis Abundant]]) protein expression is induced by stresses and protects other proteins from aggregation as a result of [[desiccation]] and [[freezing]].<ref>{{cite journal|author=Goyal, K., Walton, L. J., & Tunnacliffe, A. |title=LEA proteins prevent protein aggregation due to water stress |journal=Biochemical Journal |year=2005 |volume=388 |issue=Part 1 |pages=151–157 |url=http://www.biochemj.org/bj/388/0151/bj3880151.htm |archiveurl=https://www.webcitation.org/5il9QhYT0?url=http://www.biochemj.org/bj/388/0151/bj3880151.htm |archivedate=3 August 2009 |pmid=15631617 |doi=10.1042/BJ20041931 |pmc=1186703 |deadurl=yes |df= }}</ref>
==== Effects of freezing ====
When water freezes in plants, the consequences for the plant depend very much on whether the freezing occurs within cells (intracellularly) or outside cells in intercellular spaces.<ref name="glerum1">Glerum, C. 1985. Frost hardiness of coniferous seedlings: principles and applications. p. 107–123 ''in ''Duryea, M.L. (Ed.). Proceedings: Evaluating seedling quality: principles, procedures, and predictive abilities of major tests. Workshop, October 1984, Oregon State Univ., For. Res. Lab., Corvallis OR.</ref> Intracellular freezing, which usually kills the cell<ref name="lyons">Lyons, J.M.; Raison, J.K.; Steponkus, P.L. 1979. The plant membrane in response to low temperature: an overview. p. 1–24 ''in'' Lyons, J.M.; Graham, D.; Raison, J.K. (Eds.). Low Temperature Stress in Crop Plants. Academic Press, New York NY.</ref> regardless of the hardiness of the plant and its tissues, seldom occurs in nature because rates of cooling are rarely high enough to support it. Rates of cooling of several degrees Celsius per minute are typically needed to cause intracellular formation of ice.<ref name="mazur">Mazur, P. 1977. The role of intracellular freezing in the death of cells cooled at supraoptimal rates. Cryobiology 14:251–272.</ref> At rates of cooling of a few degrees Celsius per hour, segregation of ice occurs in intercellular spaces.<ref name="sakai4">Sakai, A.; Larcher, W. (Eds.) 1987. Frost Survival of Plants. Springer-Verlag, New York NY. 321 p.</ref> This may or may not be lethal, depending on the hardiness of the tissue. At freezing temperatures, water in the intercellular spaces of plant tissue freezes first, though the water may remain unfrozen until temperatures drop below {{convert|-7|C|F}}.<ref name="glerum1" /> After the initial formation of intercellular ice, the cells shrink as water is lost to the segregated ice, and the cells undergo freeze-drying. This dehydration is now considered the fundamental cause of freezing injury.
===DNA damage and repair===
Plants are continuously exposed to a range of biotic and abiotic stresses. These stresses often cause [[DNA damage (naturally occurring)|DNA damage]] directly, or indirectly via the generation of [[reactive oxygen species]].<ref name="pmid18707020">{{cite journal |vauthors=Roldán-Arjona T, Ariza RR |title=Repair and tolerance of oxidative DNA damage in plants |journal=Mutat. Res. |volume=681 |issue=2-3 |pages=169–79 |year=2009 |pmid=18707020 |doi=10.1016/j.mrrev.2008.07.003 |url=https://zenodo.org/record/897726}}</ref> Plants are capable of a DNA damage response that is a critical mechanism for maintaining genome stability.<ref name="pmid26617076">{{cite journal |vauthors=Yoshiyama KO |title=SOG1: a master regulator of the DNA damage response in plants |journal=Genes Genet. Syst. |volume=90 |issue=4 |pages=209–16 |year=2016 |pmid=26617076 |doi=10.1266/ggs.15-00011 |url=}}</ref> The DNA damage response is particularly important during [[seed]] [[germination]], since seed quality tends to deteriorate with age in association with DNA damage accumulation.<ref name="pmid25750428">{{cite journal |vauthors=Waterworth WM, Bray CM, West CE |title=The importance of safeguarding genome integrity in germination and seed longevity |journal=J. Exp. Bot. |volume=66 |issue=12 |pages=3549–58 |year=2015 |pmid=25750428 |doi=10.1093/jxb/erv080 |url=}}</ref> During germination repair processes are activated to deal with this accumulated DNA damage.<ref name="pmid11321247">{{cite journal |vauthors=Koppen G, Verschaeve L |title=The alkaline single-cell gel electrophoresis/comet assay: a way to study DNA repair in radicle cells of germinating Vicia faba |journal=Folia Biol. (Praha) |volume=47 |issue=2 |pages=50–4 |year=2001 |pmid=11321247 |doi= |url=}}</ref> In particular, single- and double-strand breaks in DNA can be [[DNA repair|repair]]ed.<ref name="pmid20584150">{{cite journal |vauthors=Waterworth WM, Masnavi G, Bhardwaj RM, Jiang Q, Bray CM, West CE |title=A plant DNA ligase is an important determinant of seed longevity |journal=Plant J. |volume=63 |issue=5 |pages=848–60 |year=2010 |pmid=20584150 |doi=10.1111/j.1365-313X.2010.04285.x |url=}}</ref> The DNA checkpoint kinase [[ATM serine/threonine kinase|ATM]] has a key role in integrating progression through germination with repair responses to the DNA damages accumulated by the aged seed.<ref name="pmid27503884">{{cite journal |vauthors=Waterworth WM, Footitt S, Bray CM, Finch-Savage WE, West CE |title=DNA damage checkpoint kinase ATM regulates germination and maintains genome stability in seeds |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=113 |issue=34 |pages=9647–52 |year=2016 |pmid=27503884 |pmc=5003248 |doi=10.1073/pnas.1608829113 |url=}}</ref>
=== Plant cells ===
[[File:Plant cell structure-en.svg|thumb|Plant cell structure]]
{{Main|Plant cell}}
Plant cells are typically distinguished by their large water-filled central [[vacuole]], [[chloroplast]]s, and rigid [[cell wall]]s that are made up of [[cellulose]], [[hemicellulose]], and [[pectin]]. [[Cell division]] is also characterized by the development of a [[phragmoplast]] for the construction of a [[cell plate]] in the late stages of [[cytokinesis]]. Just as in animals, plant cells differentiate and develop into multiple cell types. [[Totipotent]] [[meristem]]atic cells can differentiate into [[vascular tissue|vascular]], storage, protective (e.g. [[epidermis (botany)|epidermal layer]]), or [[plant sexuality|reproductive]] tissues, with more primitive plants lacking some tissue types.<ref name="Campbell">Campbell, Reece, ''Biology'', 7th edition, Pearson/Benjamin Cummings, 2005.</ref>
== Physiology ==
{{Main|Plant physiology}}
=== Photosynthesis ===
{{Main|Photosynthesis|Biological pigment}}
Plants are [[photosynthesis|photosynthetic]], which means that they manufacture their own food molecules using energy obtained from [[light]]. The primary mechanism plants have for capturing light energy is the [[pigment]] [[chlorophyll]]. All green plants contain two forms of chlorophyll, [[chlorophyll a|chlorophyll ''a'']] and [[chlorophyll b|chlorophyll ''b'']]. The latter of these pigments is not found in red or brown algae.
The simple equation of photosynthesis is as follows:-
6CO<sub>2</sub> + 6H<sub>2</sub>O → (in the presence of light and chlorophyll) C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> + 6O<sub>2</sub>
=== Immune system ===
{{See also|Immune system|Plant disease resistance}}
By means of cells that behave like nerves, plants receive and distribute within their systems information about incident light intensity and quality. Incident light that stimulates a chemical reaction in one leaf, will cause a chain reaction of signals to the entire plant via a type of cell termed a ''bundle sheath cell''. Researchers, from the [[Warsaw University of Life Sciences]] in Poland, found that plants have a specific memory for varying light conditions, which prepares their immune systems against seasonal pathogens.<ref>{{cite web|url=https://www.bbc.co.uk/news/10598926|title=Plants 'can think and remember'|first=Victoria|last=Gill|date=14 July 2010|publisher=|via=www.bbc.co.uk}}</ref> Plants use pattern-recognition receptors to recognize conserved microbial signatures. This recognition triggers an immune response. The first plant receptors of conserved microbial signatures were identified in rice (XA21, 1995)<ref>{{cite journal |author= Song, W.Y.|title= A receptor kinase-like protein encoded by the rice disease resistance gene, XA21 |journal= Science |volume= 270 |issue= 5243 |pages= 1804–1806 |year= 1995 |pmid= 8525370 |doi= 10.1126/science.270.5243.1804|display-authors=etal|bibcode= 1995Sci...270.1804S}}</ref> and in ''[[Arabidopsis thaliana]]'' (FLS2, 2000).<ref>{{cite journal |author= Gomez-Gomez, L.|title= FLS2: an LRR receptor-like kinase involved in the perception of the bacterial elicitor flagellin in ''Arabidopsis'' |journal= Molecular Cell |volume= 5 |issue= 6 |pages= 1003–1011 |year= 2000 |pmid= 10911994 |doi= 10.1016/S1097-2765(00)80265-8|display-authors=etal}}</ref> Plants also carry immune receptors that recognize highly variable pathogen effectors. These include the NBS-LRR class of proteins.
=== Internal distribution ===
{{Main|Vascular tissue}}
[[Vascular plant]]s differ from other plants in that nutrients are transported between their different parts through specialized structures, called [[xylem]] and [[phloem]]. They also have [[root]]s for taking up water and minerals. The xylem moves water and minerals from the root to the rest of the plant, and the phloem provides the roots with sugars and other nutrient produced by the leaves.<ref name="Campbell" />
== Genomics ==
Plants have some of the largest [[genome]]s among all organisms.<ref>{{Cite journal|last=Michael|first=Todd P.|last2=Jackson|first2=Scott|date=1 July 2013|title=The First 50 Plant Genomes|url=https://www.crops.org/publications/tpg/abstracts/6/2/plantgenome2013.03.0001in|journal=The Plant Genome|language=en|volume=6|issue=2|doi=10.3835/plantgenome2013.03.0001in|issn=1940-3372}}</ref> The largest plant genome (in terms of gene number) is that of [[wheat]] (''Triticum asestivum''), predicted to encode ~94,000 genes<ref>{{Cite journal|last=Brenchley|first=Rachel|last2=Spannagl|first2=Manuel|last3=Pfeifer|first3=Matthias|last4=Barker|first4=Gary L. A.|last5=D'Amore|first5=Rosalinda|last6=Allen|first6=Alexandra M.|last7=McKenzie|first7=Neil|last8=Kramer|first8=Melissa|last9=Kerhornou|first9=Arnaud|date=29 November 2012|title=Analysis of the bread wheat genome using whole-genome shotgun sequencing|journal=Nature|volume=491|issue=7426|pages=705–710|doi=10.1038/nature11650|issn=1476-4687|pmc=3510651|pmid=23192148|bibcode=2012Natur.491..705B}}</ref> and thus almost 5 times as many as the [[human genome]]. The first plant genome sequenced was that of ''[[Arabidopsis thaliana]]'' which encodes about 25,500 genes.<ref>{{Cite journal|last=Arabidopsis Genome Initiative|date=14 December 2000|title=Analysis of the genome sequence of the flowering plant Arabidopsis thaliana|journal=Nature|volume=408|issue=6814|pages=796–815|doi=10.1038/35048692|issn=0028-0836|pmid=11130711}}</ref> In terms of sheer DNA sequence, the smallest published genome is that of the carnivorous [[Utricularia gibba|bladderwort]] (''Utricularia gibba)'' at 82 Mb (although it still encodes 28,500 genes)<ref>{{Cite journal|last=Ibarra-Laclette|first=Enrique|last2=Lyons|first2=Eric|last3=Hernández-Guzmán|first3=Gustavo|last4=Pérez-Torres|first4=Claudia Anahí|last5=Carretero-Paulet|first5=Lorenzo|last6=Chang|first6=Tien-Hao|last7=Lan|first7=Tianying|last8=Welch|first8=Andreanna J.|last9=Juárez|first9=María Jazmín Abraham|date=6 June 2013|title=Architecture and evolution of a minute plant genome|journal=Nature|volume=498|issue=7452|pages=94–98|doi=10.1038/nature12132|issn=1476-4687|pmc=4972453|pmid=23665961|bibcode=2013Natur.498...94I}}</ref> while the largest, from the [[Picea abies|Norway Spruce]] (''Picea abies''), extends over 19,600 Mb (encoding about 28,300 genes).<ref>{{Cite journal|last=Nystedt|first=Björn|last2=Street|first2=Nathaniel R.|last3=Wetterbom|first3=Anna|last4=Zuccolo|first4=Andrea|last5=Lin|first5=Yao-Cheng|last6=Scofield|first6=Douglas G.|last7=Vezzi|first7=Francesco|last8=Delhomme|first8=Nicolas|last9=Giacomello|first9=Stefania|date=30 May 2013|title=The Norway spruce genome sequence and conifer genome evolution|journal=Nature|volume=497|issue=7451|pages=579–584|doi=10.1038/nature12211|issn=1476-4687|pmid=23698360|bibcode=2013Natur.497..579N}}</ref>
== Ecology ==
{{Main|Plant ecology}}
The photosynthesis conducted by land plants and algae is the ultimate source of energy and organic material in nearly all ecosystems. Photosynthesis, at first by cyanobacteria and later by photosynthetic eukaryotes, radically changed the composition of the early Earth's anoxic atmosphere, which as a result is now 21% [[oxygen]]. Animals and most other organisms are [[Aerobic organism|aerobic]], relying on oxygen; those that do not are confined to relatively rare [[anaerobic environment]]s. Plants are the [[Autotroph|primary producers]] in most terrestrial ecosystems and form the basis of the [[food web]] in those ecosystems. Many animals rely on plants for shelter as well as oxygen and food.
Land plants are key components of the [[water cycle]] and several other [[biogeochemical cycle]]s. Some plants have [[coevolve]]d with [[nitrogen fixation|nitrogen fixing]] bacteria, making plants an important part of the [[nitrogen cycle]]. Plant roots play an essential role in [[soil]] development and the prevention of [[soil erosion]].
=== Distribution ===
{{Expand section|date=June 2008}}
Plants are distributed almost worldwide. While they inhabit a multitude of [[biome]]s and [[ecoregion]]s, few can be found beyond the [[tundra]]s at the northernmost regions of [[continental shelf|continental shelves]]. At the southern extremes, plants have adapted tenaciously to the prevailing conditions. (See [[Antarctic flora]].)
Plants are often the dominant physical and structural component of habitats where they occur. Many of the Earth's [[biome]]s are named for the type of vegetation because plants are the dominant organisms in those biomes, such as [[grassland]]s, [[taiga]] and [[tropical rainforest]].
=== Ecological relationships ===
[[File:Venus Flytrap showing trigger hairs.jpg|thumb|The [[Venus flytrap]], a species of [[carnivorous plant]].]]
Numerous animals have coevolved with plants. Many animals [[pollination|pollinate]] [[flower]]s in exchange for food in the form of pollen or [[nectar]]. Many animals [[biological dispersal|disperse seeds]], often by eating [[fruit]] and passing the seeds in their [[feces]]. [[Myrmecophyte]]s are plants that have coevolved with [[ant]]s. The plant provides a home, and sometimes food, for the ants. In exchange, the ants defend the plant from [[herbivore]]s and sometimes competing plants. Ant wastes provide organic [[fertilizer]].
The majority of plant species have various kinds of fungi associated with their root systems in a kind of [[Mutualism (biology)|mutualistic]] [[symbiosis]] known as [[mycorrhiza]]. The fungi help the plants gain water and mineral nutrients from the soil, while the plant gives the fungi carbohydrates manufactured in photosynthesis. Some plants serve as homes for [[endophyte|endophytic]] fungi that protect the plant from herbivores by producing toxins. The fungal endophyte, ''[[Neotyphodium coenophialum]]'', in [[tall fescue]] (''Festuca arundinacea'') does tremendous economic damage to the cattle industry in the U.S.
Various forms of parasitism are also fairly common among plants, from the semi-parasitic [[mistletoe]] that merely takes some nutrients from its host, but still has photosynthetic leaves, to the fully parasitic [[Orobanche|broomrape]] and [[Lathraea|toothwort]] that acquire all their nutrients through connections to the roots of other plants, and so have no [[chlorophyll]]. Some plants, known as [[myco-heterotroph]]s, parasitize mycorrhizal fungi, and hence act as [[epiparasite]]s on other plants.
Many plants are [[epiphyte]]s, meaning they grow on other plants, usually trees, without parasitizing them. Epiphytes may indirectly harm their host plant by intercepting mineral nutrients and light that the host would otherwise receive. The weight of large numbers of epiphytes may break tree limbs. [[Hemiepiphyte]]s like the [[strangler fig]] begin as epiphytes but eventually set their own roots and overpower and kill their host. Many [[orchid]]s, [[bromeliad]]s, [[fern]]s and [[moss]]es often grow as epiphytes. Bromeliad epiphytes accumulate water in leaf axils to form [[phytotelma]]ta that may contain complex aquatic food webs.<ref>Howard Frank, [http://entomology.ifas.ufl.edu/frank/bromeliadbiota/bromfit.htm Bromeliad Phytotelmata], October 2000</ref>
Approximately 630 plants are [[carnivorous plant|carnivorous]], such as the [[Venus Flytrap]] (''Dionaea muscipula'') and [[sundew]] (''Drosera'' species). They trap small animals and digest them to obtain mineral nutrients, especially [[nitrogen]] and [[phosphorus]].<ref name="Barthlott">Barthlott, W., S. Porembski, R. Seine, and I. Theisen. 2007. ''The Curious World of Carnivorous Plants: A Comprehensive Guide to Their Biology and Cultivation.'' Timber Press: Portland, Oregon.</ref>
== Importance ==
{{Main|Plants in culture}}
The study of plant uses by people is called economic botany or [[ethnobotany]].<ref>{{Cite book|url=https://books.google.com/books?id=_wS-DAAAQBAJ&pg=PA644 |title=Economic Botany: A Comprehensive Study |last=Kochhar |first=S. L.|date=31 May 2016 |publisher=Cambridge University Press |isbn=9781316675397}}</ref> Human cultivation of plants is part of [[agriculture]], which is the basis of human civilization.<ref>{{Cite book|url=https://books.google.com/books?id=xtg672jRCfAC&pg=RA1-PA9 |title=Workplace Communication for the 21st Century: Tools and Strategies that Impact the Bottom Line [2 volumes]: Tools and Strategies That Impact the Bottom Line |author=Wrench, Jason S. |date=9 January 2013|publisher=ABC-CLIO|isbn=9780313396328}}</ref> Plant agriculture is subdivided into [[agronomy]], [[horticulture]] and [[forestry]].<ref>{{Cite book |url=https://books.google.com/books?id=wiVGAQAAMAAJ&pg=PA429 |title=Report on the Agricultural Experiment Stations |author=United States Agricultural Research Service |date=1903 |publisher=U.S. Government Printing Office|language=en}}</ref>
=== Food ===
[[File:Harvest Time - geograph.org.uk - 747095.jpg|thumb|Mechanical harvest of oats.]]
{{Main|Agriculture}}
Humans depend on plants for [[food]], either directly or as feed for [[domestic animal]]s. [[Agriculture]] deals with the production of food crops, and has [[History of agriculture|played a key role in the history of world civilizations]]. Agriculture includes [[agronomy]] for arable crops, [[horticulture]] for vegetables and fruit, and [[forestry]] for timber.<ref name=NatGeogAgriculture>{{cite web |title=The Development of Agriculture |url=https://genographic.nationalgeographic.com/development-of-agriculture/ |publisher=[[National Geographic Society|National Geographic]] |accessdate=2017-10-01 |date=2016 |deadurl=yes |archiveurl=https://web.archive.org/web/20160414142437/https://genographic.nationalgeographic.com/development-of-agriculture/ |archivedate=14 April 2016 |df=dmy-all }}</ref> About 7,000 species of plant have been used for food, though most of today's food is derived from only 30 species. The major [[staple crop|staples]] include [[cereal]]s such as [[rice]] and [[wheat]], starchy roots and tubers such as [[cassava]] and [[potato]], and [[legume]]s such as [[peas]] and [[bean]]s. [[Vegetable oil]]s such as [[olive oil]] provide [[lipids]], while [[fruit]] and [[vegetable]]s contribute [[vitamin]]s and minerals to the diet.<ref>{{cite web |title=Food and drink |url=http://www.kew.org/science-conservation/plants-fungi/food-drink |publisher=[[Kew Gardens]] |accessdate=2017-10-01 |deadurl=yes |archiveurl=https://web.archive.org/web/20140328124344/http://www.kew.org/science-conservation/plants-fungi/food-drink |archivedate=28 March 2014}}</ref>
=== Medicines ===
{{main|Medicinal plants}}
[[Medicinal plants]] are a primary source of [[organic compound]]s, both for their medicinal and physiological effects, and for the industrial [[organic synthesis|synthesis]] of a vast array of organic chemicals.<ref>{{cite web|title=Chemicals from Plants|publisher=Cambridge University Botanic Garden |url=http://www.botanic.cam.ac.uk/Botanic/Trail.aspx?p=27&ix=11 |accessdate=9 December 2017}} Note that the details of each plant and the chemicals it yields are described in the linked subpages.</ref> Many hundreds of medicines are derived from plants, both traditional medicines used in [[herbalism]]<ref name="tapsell">{{cite journal |vauthors=Tapsell LC, Hemphill I, Cobiac L |title=Health benefits of herbs and spices: the past, the present, the future |journal=Med. J. Aust. |volume=185 |issue=4 Suppl |pages=S4–24 |date=August 2006 |pmid=17022438 |doi= |url= |displayauthors=etal }}</ref><ref name="lai">{{cite journal |author=Lai PK, Roy J |title=Antimicrobial and chemopreventive properties of herbs and spices |journal=Curr. Med. Chem. |volume=11 |issue= 11|pages=1451–60 |date=June 2004 |pmid=15180577 |doi= 10.2174/0929867043365107|url=|last2=Roy }}</ref> and chemical substances purified from plants or first identified in them, sometimes by [[ethnobotany|ethnobotanical]] search, and then [[organic synthesis|synthesised]] for use in modern medicine. Modern medicines derived from plants include [[aspirin]], [[taxol]], [[morphine]], [[quinine]], [[reserpine]], [[colchicine]], [[digitalis]] and [[vincristine]]. [[List of plants used in herbalism|Plants used in herbalism]] include [[Ginkgo biloba|ginkgo]], [[echinacea]], [[feverfew]], and [[Saint John's wort]]. The [[pharmacopoeia]] of [[Dioscorides]], ''[[De Materia Medica]]'', describing some 600 medicinal plants, was written between 50 and 70 AD and remained in use in Europe and the Middle East until around 1600 AD; it was the precursor of all modern pharmacopoeias.<ref name=NIH>{{cite web | url=https://www.nlm.nih.gov/hmd/greek/greek_dioscorides.html | title=Greek Medicine | publisher=National Institutes of Health, USA | date=16 September 2002 | accessdate=22 May 2014}}</ref><ref>{{cite book | url=https://books.google.com/books?id=iORoAgAAQBAJ&pg=PA46&lpg=PA46 | author=Hefferon, Kathleen | title=Let Thy Food Be Thy Medicine | publisher=Oxford University Press | date=2012 |page=46}}</ref><ref>{{cite book | url=https://books.google.com/books?id=jBMEAwAAQBAJ&pg=PT143&lpg=PT143 | author=Rooney, Anne | title=The Story of Medicine | publisher=Arcturus Publishing | date=2009 | page=143}}</ref>
=== Nonfood products ===
[[File:Timber DonnellyMills2005 SeanMcClean.jpg|thumb|[[Timber]] in storage for later processing at a [[sawmill]]]]
Plants grown as [[industrial crop]]s are the source of a wide range of products used in manufacturing, sometimes so intensively as to risk harm to the environment.<ref>{{cite web |title=Industrial Crop Production |url=http://www.sustainabletable.org/804/industrial-crop-production |publisher=Grace Communications Foundation |accessdate=2016-06-20|date=2016}}</ref> Nonfood products include [[essential oil]]s, [[natural dye]]s, pigments, waxes, [[resin]]s, [[tannin]]s, alkaloids, amber and [[Cork material|cork]]. Products derived from plants include soaps, shampoos, perfumes, cosmetics, paint, varnish, turpentine, rubber, [[latex]], lubricants, linoleum, plastics, inks, and [[Gum (botany)|gums]]. Renewable fuels from plants include [[firewood]], [[peat]] and other [[biofuel]]s.<ref>{{cite web |title=INDUSTRIAL CROPS AND PRODUCTS An International Journal |url=https://www.elsevier.com/journals/industrial-crops-and-products/0926-6690?generatepdf=true |publisher=Elsevier |accessdate=2016-06-20}}</ref><ref name="CruzDierig2014">{{cite book |last1=Cruz |first1=Von Mark V. |last2=Dierig |first2=David A. |title=Industrial Crops: Breeding for BioEnergy and Bioproducts |url=https://books.google.com/books?id=iIFxBQAAQBAJ&pg=PR9 |year=2014 |publisher=Springer |isbn=978-1-4939-1447-0 |pages=9 and passim}}</ref> The [[fossil fuel]]s [[coal]], [[petroleum]] and [[natural gas]] are derived from the remains of aquatic organisms including [[phytoplankton]] in [[geological time]].<ref>{{cite book |last1=Sato |first1=Motoaki |title=Thermochemistry of the formation of fossil fuels |work=Fluid-Mineral Interactions: A Tribute to H. P. Eugster, Special Publication No.2 |date=1990 |url=http://www.geochemsoc.org/files/6214/1261/1770/SP-2_271-284_Sato.pdf |publisher=The Geochemical Society}}</ref>
Structural resources and fibres from plants are used to construct dwellings and to manufacture clothing. [[Wood]] is used not only for buildings, boats, and furniture, but also for smaller items such as [[musical instrument]]s and sports equipment. Wood is [[Pulp (paper)|pulped]] to make paper and cardboard.<ref>{{cite book |title=Handbook of pulp |volume=1 |editor1-last=Sixta |editor1-first=Herbert |year=2006 |publisher=Wiley-VCH |location=Winheim, Germany |isbn=3-527-30997-7 |page=9}}</ref> Cloth is often made from [[cotton]], [[flax]], [[ramie]] or synthetic fibres such as [[rayon]] and [[acetate]] derived from plant [[cellulose]]. [[Thread (yarn)|Thread]] used to sew cloth likewise comes in large part from cotton.<ref>{{cite web |title=Natural fibres |url=http://www.naturalfibres2009.org/en/fibres/|website=Discover Natural Fibres |accessdate=2016-06-20}}</ref>
=== Aesthetic uses ===
{{refimprove section|date=June 2016}}
[[File:Rose espalier Niedernhall.JPG|thumb|left|A rose [[espalier]] at Niedernhall in Germany.]]
Thousands of plant species are cultivated for aesthetic purposes as well as to provide shade, modify temperatures, reduce wind, abate noise, provide privacy, and prevent soil erosion. Plants are the basis of a multibillion-dollar per year tourism industry, which includes travel to [[garden tourism|historic gardens]], [[national park]]s, [[rainforest]]s, [[forest]]s with colorful autumn leaves, and festivals such as [[Hanami|Japan's]]<ref>{{cite book |url= https://books.google.com/books?id=T2blg2Kw_zcC&pg=PA12&dq=hanami#v=onepage&q=hanami&f=false |page=12 |title=Introduction to Japanese culture |first=Daniel |last=Sosnoski |publisher=Tuttle |year=1996 |isbn=0-8048-2056-2}}</ref> and [[National Cherry Blossom Festival|America's cherry blossom festivals]].<ref name="NCBF">{{cite web |archiveurl=https://web.archive.org/web/20160314055554/http://www.nationalcherryblossomfestival.org/about/history/ |archivedate=14 March 2016 |url=http://www.nationalcherryblossomfestival.org/about/history/ |title=History of the Cherry Blossom Trees and Festival |work=National Cherry Blossom Festival: About |publisher=National Cherry Blossom Festival |accessdate=22 March 2016}}</ref>
[[File:Luxor, West Bank, Ramesseum, column top decorations, Egypt, Oct 2004.jpg|thumb|Capitals of ancient Egyptian columns decorated to resemble [[Cyperus papyrus|papyrus]] plants. (at Luxor, Egypt)]]
While some [[garden]]s are planted with food crops, many are planted for aesthetic, ornamental, or conservation purposes. [[Arboretum]]s and [[botanical garden]]s are public collections of living plants. In private outdoor gardens, lawn grasses, shade trees, ornamental trees, shrubs, vines, herbaceous perennials and bedding plants are used. Gardens may cultivate the plants in a naturalistic state, or may sculpture their growth, as with [[topiary]] or [[espalier]]. [[Gardening]] is the most popular leisure activity in the U.S., and working with plants or [[horticulture therapy]] is beneficial for rehabilitating people with disabilities.
Plants may also be grown or kept indoors as [[houseplant]]s, or in specialized buildings such as [[greenhouse]]s that are designed for the care and cultivation of living plants. [[Venus Flytrap]], [[sensitive plant]] and [[resurrection plant]] are examples of plants sold as novelties. There are also art forms specializing in the arrangement of cut or living plant, such as [[bonsai]], [[ikebana]], and the arrangement of cut or dried flowers. [[Ornamental plant]]s have sometimes changed the course of history, as in [[tulip mania|tulipomania]].<ref name="Lambert">{{cite web|last1=Lambert|first1=Tim|title=A Brief History of Gardening|url=http://www.localhistories.org/gardening.html|publisher=[[British Broadcasting Corporation]]|accessdate=21 June 2016|date=2014}}</ref>
Architectural designs resembling plants appear in the capitals of [[Ancient Egypt]]ian columns, which were carved to resemble either the [[Nymphaea lotus|Egyptian white lotus]] or the [[Cyperus papyrus|papyrus]].<ref>{{cite book |last=Wilkinson |first=Richard H. |authorlink=Richard H. Wilkinson |title=The Complete Temples of Ancient Egypt |year=2000 |publisher=Thames and Hudson |isbn=0-500-05100-3 | pages=65–66}}</ref> Images of plants are often used in painting and photography, as well as on textiles, money, stamps, flags and coats of arms.
=== Scientific and cultural uses ===
[[File:Barbara McClintock (1902-1992).jpg|thumb|Barbara McClintock (1902–1992) was a pioneering [[cytogenetics|cytogeneticist]] who used [[maize]] (or corn) to study the mechanism of inheritance of traits.]]
Basic biological research has often been done with plants. In [[genetics]], the breeding of pea plants allowed [[Gregor Mendel]] to derive the basic laws governing inheritance,<ref>{{cite web |title=Mendel's Paper in English |url=http://www.mendelweb.org/Mendel.html |first=Roger B. |last=Blumberg}}</ref> and examination of [[chromosome]]s in maize allowed [[Barbara McClintock]] to demonstrate their connection to inherited traits.<ref>{{cite web |title=BARBARA McCLINTOCK:A Brief Biographical Sketch |url=http://library.cshl.edu/archives/archives/bmcbio.htm |publisher=WebCite |accessdate=21 June 2016 |deadurl=yes |archiveurl=https://www.webcitation.org/615y4NCQG?url=http://library.cshl.edu/archives/archives/bmcbio.htm |archivedate=21 August 2011 |df=dmy-all }}</ref> The plant ''[[Arabidopsis thaliana]]'' is used in laboratories as a [[model organism]] to understand how [[gene]]s control the growth and development of plant structures.<ref>{{cite web |title=About Arabidopsis |url=http://www.arabidopsis.org/portals/education/aboutarabidopsis.jsp |publisher=TAIR |accessdate=21 June 2016}}</ref> [[NASA]] predicts that space stations or space colonies will one day rely on plants for [[Controlled Ecological Life Support System|life support]].<ref>{{cite web |title=Engineering Life |url=http://settlement.arc.nasa.gov/Contest/Results/96/winner/seis.html |publisher=[[NASA]] |accessdate=21 June 2016}}</ref>
Ancient trees are revered and many are [[List of famous trees|famous]]. [[Tree ring]]s themselves are an important method of dating in archeology, and serve as a record of past climates.
Plants figure prominently in [[Trees in mythology|mythology]], religion and [[List of fictional plants|literature]]. They are used as [[National emblem|national]] and state emblems, including [[List of U.S. state trees|state trees]] and [[state flower]]s. Plants are often used as memorials, gifts and to mark special occasions such as births, deaths, weddings and holidays. The arrangement of flowers may be used to send hidden [[Language of flowers|messages]].
=== Negative effects ===
[[Weed]]s are unwanted plants growing in managed environments such as [[agriculture|farms]], [[urban area]]s, [[garden]]s, [[lawn]]s, and [[park]]s. People have spread plants beyond their native ranges and some of these introduced plants become [[invasive species|invasive]], damaging existing ecosystems by displacing native species, and sometimes becoming serious weeds of cultivation.
Plants may cause harm to animals, including people. Plants that produce [[anemophily|windblown pollen]] invoke allergic reactions in people who suffer from [[hay fever]]. A wide variety of plants are [[List of poisonous plants|poisonous]]. [[Toxalbumin]]s are plant poisons fatal to most mammals and act as a serious deterrent to consumption. Several plants cause skin irritations when touched, such as [[poison ivy]]. Certain plants contain [[psychotropic]] [[secondary metabolite|chemicals]], which are extracted and ingested or smoked, including [[nicotine]] from [[tobacco]], [[cannabinoids]] from [[Cannabis sativa]], [[cocaine]] from [[Erythroxylon coca]] and [[opium]] from [[opium poppy]]. [[Smoking]] causes damage to health or even death, while some drugs may also be harmful or fatal to people.<ref>{{cite web|url=http://www.urban75.com/Drugs/drugcoke.html |title=cocaine/crack}}</ref><ref>{{cite web |url=http://ar2005.emcdda.europa.eu/en/page050-en.html |title=Deaths related to cocaine}}</ref> Both illegal and legal drugs derived from plants may have negative effects on the economy, affecting worker productivity and law enforcement costs.<ref>{{cite web |url=http://www.whitehousedrugpolicy.gov/NEWS/press02/012302.html |archiveurl=https://web.archive.org/web/20080215071055/http://www.whitehousedrugpolicy.gov/NEWS/press02/012302.html |archivedate=15 February 2008 |title=Illegal drugs drain $160 billion a year from American economy}}</ref><ref>{{cite web|url=http://www.ingentaconnect.com/content/bsc/add/2002/00000097/00000009/art00012 |title=The social cost of illegal drug consumption in Spain}}</ref> Some plants cause allergic reactions when ingested, while other plants cause food intolerances that negatively affect health.
== See also ==
{{Wikipedia books|Plants}}
{{div col|colwidth=30em}}
* [[Biosphere]]
* [[DPVweb]]
* [[Evolutionary history of plants]]
* [[Leaf sensor]]
* [[Plant cognition]]
* [[Plant defense against herbivory]]
* [[Plant identification]]
* [[Plants in space]]
* [[The Plant List]]
{{div col end}}
== References ==
{{Reflist|colwidth=30em}}
== Further reading ==
;General:
* Evans, L. T. (1998). ''Feeding the Ten Billion – Plants and [[Population]] Growth''. [[Cambridge University Press]]. Paperback, 247 pages. {{ISBN|0-521-64685-5}}.
* Kenrick, Paul & Crane, Peter R. (1997). ''The Origin and Early Diversification of Land Plants: A Cladistic Study''. Washington, D. C.: Smithsonian Institution Press. {{ISBN|1-56098-730-8}}.
* Raven, Peter H., Evert, Ray F., & Eichhorn, Susan E. (2005). ''Biology of Plants'' (7th ed.). New York: W. H. Freeman and Company. {{ISBN|0-7167-1007-2}}.
* Taylor, Thomas N. & Taylor, Edith L. (1993). ''The Biology and Evolution of Fossil Plants''. Englewood Cliffs, NJ: Prentice Hall. {{ISBN|0-13-651589-4}}.
* {{cite journal |author= Trewavas A |year= 2003 |title= Aspects of Plant Intelligence |url= http://aob.oxfordjournals.org/cgi/content/full/92/1/1 |journal= Annals of Botany |volume= 92 |issue= 1 |pages= 1–20 |doi= 10.1093/aob/mcg101 |pmid=12740212 |pmc=4243628}}
;Species estimates and counts:
* International Union for Conservation of Nature and Natural Resources (IUCN) Species Survival Commission (2004). [[IUCN Red List]] [http://www.iucnredlist.org/].
* {{cite journal |author= Prance G. T. |year= 2001 |title= Discovering the Plant World |journal= Taxon |volume= 50 |issue= 2, Golden Jubilee Part 4 |pages= 345–359 |publisher= International Association for Plant Taxonomy |issn= 0040-0262 |doi=10.2307/1223885 |jstor=1223885}}
== External links ==
{{Wikibooks|Dichotomous Key|Plantae}}
* {{cite journal|author=Jones, T. M., Reid, C. S., Urbatsch, L. E|title=Visual study of divisional Plantae|url=http://www.herbarium.lsu.edu/keys/aca/}} (requires [[Microsoft Silverlight]])
* {{cite journal|author=Chaw, S.-M.|url=http://mbe.library.arizona.edu/data/1997/1401/7chaw.pdf|title=Molecular Phylogeny of Extant Gymnosperms and Seed Plant Evolution: Analysis of Nuclear 18s rRNA Sequences|journal=Mol. Biol. Evol.|volume=14|issue=1|pages=56–68|year=1997|pmid=9000754|doi=10.1093/oxfordjournals.molbev.a025702|display-authors=etal|deadurl=yes|archiveurl=https://web.archive.org/web/20050124004310/http://mbe.library.arizona.edu/data/1997/1401/7chaw.pdf|archivedate=24 January 2005|df=dmy-all}}
* [http://ucjeps.berkeley.edu/INA.html Index Nominum Algarum]
* [https://web.archive.org/web/20060210225113/http://florabase.calm.wa.gov.au/phylogeny/cronq88.html Interactive Cronquist classification]
* [http://www.prota.org/uk/About+Prota/ Plant Resources of Tropical Africa]
* [http://tolweb.org/Green_plants Tree of Life]
;Botanical and vegetation databases
* [http://www.ville-ge.ch/musinfo/bd/cjb/africa/recherche.php?langue=an African Plants Initiative database]
* [http://www.anbg.gov.au/cpbr/databases/ Australia]
* [http://www.chilebosque.cl/ Chilean plants at ''Chilebosque'']
* [http://www.efloras.org/index.aspx e-Floras (Flora of China, Flora of North America and others)]
* [http://rbg-web2.rbge.org.uk/FE/fe.html Flora Europaea]
* [http://www.floraweb.de/ Flora of Central Europe] {{de icon}}
* [http://www.efloras.org/flora_page.aspx?flora_id=1 Flora of North America]
* [http://www.alpine-plants-jp.com/botanical_name/list_of_japanese_wild_plants_abelia_buxus.htm List of Japanese Wild Plants Online]
* [https://web.archive.org/web/20070616151737/http://ntbg.org/plants/choose_a_plant.php Meet the Plants-National Tropical Botanical Garden]
* [http://www.wildflower.org/ Lady Bird Johnson Wildflower Center – Native Plant Information Network at University of Texas, Austin]
* [http://www.theplantlist.org/ The Plant List]
* [http://plants.usda.gov/ United States Department of Agriculture] not limited to continental US species
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