Difference between revisions of "Plants"

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{{Taxobox
 
{{Taxobox
 
| color = lightgreen
 
| color = lightgreen
 
| name = Plants
 
| name = Plants
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| fossil_range = {{fossil range|520}}[[Cambrian]] to recent, but [[#Fossils|see text]]
 
 
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** [[Hornwort|Anthocerotophyta]]—hornworts
 
** [[Hornwort|Anthocerotophyta]]—hornworts
 
** [[Moss|Bryophyta]]—mosses
 
** [[Moss|Bryophyta]]—mosses
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** †[[Horneophytopsida]]
 
 
* '''[[Vascular plant]]s (tracheophytes)'''
 
* '''[[Vascular plant]]s (tracheophytes)'''
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** †[[Rhyniophyta]]—rhyniophytes
 
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** †[[Zosterophyllophyta]]—zosterophylls
 
 
** [[Lycopodiophyta]]—clubmosses
 
** [[Lycopodiophyta]]—clubmosses
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** †[[Trimerophytophyta]]—trimerophytes
 
 
** [[fern|Pteridophyta]]—ferns and horsetails
 
** [[fern|Pteridophyta]]—ferns and horsetails
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** †[[Progymnospermophyta]]
 
 
** '''[[Spermatophyta|Seed plants]] (spermatophytes)'''
 
** '''[[Spermatophyta|Seed plants]] (spermatophytes)'''
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*** †[[Pteridospermatophyta]]—seed ferns
 
 
*** [[Pinophyta]]—conifers
 
*** [[Pinophyta]]—conifers
 
*** [[Cycad]]ophyta—cycads
 
*** [[Cycad]]ophyta—cycads
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*** [[Gnetae|Gnetophyta]]—gnetae
 
*** [[Gnetae|Gnetophyta]]—gnetae
 
*** [[Flowering plant|Magnoliophyta]]—flowering plants
 
*** [[Flowering plant|Magnoliophyta]]—flowering plants
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† '''[[Nematophytes]]'''
 
 
}}
 
}}
  
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'''Plants''' are a major group of [[life]] forms and include familiar [[organism]]s such as [[tree]]s, <!--[[flower]]s, if flowers are plants, noses are animals -->[[herb]]s, [[bushes]], [[grasses]], [[vine]]s, [[fern]]s, [[moss]]es, and green [[alga]]e. About 350,000 [[species]] of plants, defined as [[seed plant]]s, [[bryophyte]]s, [[fern]]s and [[fern allies]], are estimated to exist currently. As of 2004, some 287,655 species had been identified, of which 258,650 are [[flowering]] and 15,000 [[bryophytes]]. '''Green plants''', sometimes called '''metaphytes''', obtain most of their energy from [[Electromagnetic radiation|sunlight]] via a process called [[photosynthesis]].  
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'''Plants''' are one of the five kingdoms used to classify all life.  The plant kingdom, known as Plantae is divided into progressively smaller subgroups, usually based on their family tree.  The primary division is between vascular and non-vascular plants - with the vascular plants being of most interest to gardeners.
  
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==Definition==
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==Non-vascular versus vascular==
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[[Aristotle]] divided all living things between plants (which generally do not move), and animals (which often are mobile to catch their food). In [[Carolus Linnaeus|Linnaeus]]' system, these became the [[kingdom (biology)|Kingdoms]] [[Vegetabilia]] (later Metaphyta or Plantae) and [[Animalia]] (also called [[Metazoa]]). Since then, it has become clear that the Plantae as originally defined included several unrelated groups, and the [[fungus|fungi]] and several groups of [[alga]]e were removed to new kingdoms. However, these are still often considered plants in many contexts, both technical and popular. Indeed, an attempt to perfectly match "plant" with a single [[taxon]] is problematic, because for most people the term "plant" is only vaguely related to the [[Phylogenetics|phylogenic]] concepts on which modern [[taxonomy]] and [[systematics]] are based.
 
  
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When the name Plantae is applied to a specific taxon, it is usually referring to one of three concepts. From smallest to largest in inclusiveness, these three groupings are:
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==Plants that bear seed==
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* [[Land plant]]s, also known as [[Embryophyta]] or Metaphyta. As the narrowest of plant categories, this is further delineated below.
 
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* '''Green plants''' -- also known as '''Viridiplantae''', '''Viridiphyta'''  or '''Chlorobionta''' -- comprise the above Embryophytes, [[Charophyta]] (i.e., primitive [[stonewort]]s), and [[Chlorophyta]] (i.e., [[green algae]] such as [[sea lettuce]]). It is this [[clade]] which is mainly the subject of this article.
 
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* [[Primoplantae]] -- also known as Plantae ''[[sensu lato]]'', [[Plastida]], or [[Archaeplastida]] -- comprises the green plants above, [[Rhodophyta]] ([[red algae]]) and [[Glaucophyta]] (simple [[glaucophyte]] algae). As the broadest plant [[clade]], this comprises most of the [[eukaryote]]s that eons ago acquired their [[chloroplast]]s directly by engulfing [[cyanobacteria]].
 
  
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Informally, other creatures that carry out photosynthesis are called plants as well, but they do not constitute a formal taxon and represent species that are not closely related to true plants. There are around about 375,000 species (types) of plants, and each year more are found and described by science.
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==Lifespan==
  
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===Algae===
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==Plant classification and nomenclature==
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[[Image:Haeckel Siphoneae.jpg|250px|thumb|[[Green algae]] from [[Ernst Haeckel]]'s ''[[Kunstformen der Natur]]'', 1904.]]
 
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{{main|Algae}}
 
  
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The [[alga]]e comprise several different groups of organisms that produce energy through photosynthesis. However, most are not classified within the Kingdom Plantae but in the Kingdom [[Protista]]. Most conspicuous are the [[seaweed]]s, multicellular algae that may roughly resemble terrestrial plants, but are classified among the [[green alga|green]], [[red alga|red]], and [[brown alga]]e. These and other algal groups also include various single-celled organisms.
+
==Species, hybrids and cultivars==
  
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The embryophytes developed from green algae ([[Chlorophyta]]); the two groups are collectively referred to as the green plants or Viridiplantae. The Kingdom Plantae is often taken to mean this [[monophyletic]] grouping. With a few exceptions among the green algae, all such forms have cell walls containing [[cellulose]] and [[chloroplast]]s containing [[chlorophyll]]s ''a'' and ''b'', and store food in the form of [[starch]]. They undergo closed [[mitosis]] without [[centriole]]s, and typically have [[mitochondrion|mitochondria]] with flat cristae.
+
==Monocots and dicots==
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The [[chloroplasts]] of green plants are surrounded by two membranes, suggesting they originated directly from endosymbiotic [[cyanobacteria]]. The same is true of the [[red alga]]e, and the two groups are generally believed to have a common origin (see [[Archaeplastida]]). In contrast, most other algae have chloroplasts with three or four membranes. They are not close relatives of the green plants, presumably in origin acquiring chloroplasts separately from ingested or symbiotic green and red algae.
 
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===Fungi===
 
−
{{main|Fungi}}
 
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[[Fungus|Fungi]] are no longer considered to be plants, though they were previously included in the plant kingdom.  Unlike embryophytes and algae, fungi are not photosynthetic, but are [[saprotrophs]]: obtaining food by breaking down and absorbing surrounding materials. Fungi are not plants, but were historically treated as closely related to plants, and were considered to be in the purview of botanists. It has long been recognized that fungi are evolutionarily closer to animals than to plants, but they still are covered more in depth in introductory botany courses and are not necessarily touched upon in introductory zoology courses. Most fungi are formed by microscopic structures called [[hyphae]], which may or may not be divided into cells but contain [[eukaryotic]] [[cell nucleus|nuclei]]. Fruiting bodies, of which [[mushroom]]s are most familiar, are the reproductive structures of fungi. They are not related to any of the photosynthetic groups, but are close relatives of [[animal]]s. Therefore, the [[fungi]] are in a kingdom of their own.
 
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==Diversity==
 
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About 350,000 [[species]] of plants, defined as [[seed plant]]s, [[bryophyte]]s, [[fern]]s and [[fern allies]], are estimated to exist currently. As of 2004, some 287,655 species had been identified, of which 258,650 are [[flowering plant]]s, 16,000 [[bryophyte]]s, 11,000 [[fern]]s and 8,000 [[green algae]].
 
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{| class="wikitable" align="left" style="margin-left:1em"
 
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|+'''Diversity of living plant divisions'''
 
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|-
 
−
! style="background:lightgreen" align="center" | Informal group
 
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! style="background:lightgreen" align="center" | Division name
 
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! style="background:lightgreen" align="center" | Common name
 
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! style="background:lightgreen" align="center" | No. of living species
 
−
|-
 
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| rowspan=2 style="background:lightgray" valign="top" | [[Green algae]]
 
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| '''[[Chlorophyta]]'''
 
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| align="left" | [[green algae]] (chlorophytes)
 
−
| align="right" | 3,800 <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>
 
−
|-
 
−
| '''[[Charophyta]]'''
 
−
| align="left" | [[green algae]] ([[desmid]]s & charophytes)
 
−
| align="right" | 4,000 - 6,000 <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:lightgray" valign="top" | [[Bryophyte]]s
 
−
| '''[[Marchantiophyta]]'''
 
−
| align="left" | liverworts
 
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| 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>
 
−
|-
 
−
| '''[[Anthocerotophyta]]'''
 
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| align="left" | hornworts
 
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| 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 0-914-86821-7.</ref>
 
−
|-
 
−
| '''[[Moss|Bryophyta]]'''
 
−
| align="left" | mosses
 
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| align="right" | 10,000 <ref>Buck, William R. & Bernard Goffinet, 2000. "Morphology and classification of mosses", page 71 ''in'' A. Jonathan Shaw & Bernard Goffinet (Eds.), ''Bryophyte Biology''. (Cambridge: Cambridge University Press). ISBN 0-521-66097-1</ref>
 
−
|-
 
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| rowspan=2 style="background:lightgray" valign="top" | [[Pteridophyte]]s
 
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| '''[[Lycopodiophyta]]'''
 
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| align="left" | club mosses
 
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| align="right" | 1,200 <ref name="Raven 2005">Raven, Peter H., Ray F. Evert, & Susan E. Eichhorn, 2005. ''Biology of Plants'', 7th edition. (New York: W. H. Freeman and Company). ISBN 0-7167-1007-2.</ref>
 
−
|-
 
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| '''[[Pteridophyta]]'''
 
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| align="left" | ferns, whisk ferns & horsetails
 
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| align="right" | 11,000 <ref name="Raven 2005" />
 
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|-
 
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| rowspan=5 style="background:lightgray" valign="top" | [[Seed plant]]s
 
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| '''[[Cycadophyta]]'''
 
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| align="left" | cycads
 
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| align="right" | 160 <ref>Gifford, Ernest M. & Adriance S. Foster, 1988. ''Morphology and Evolution of Vascular Plants'', 3rd edition, page 358. (New York: W. H. Freeman and Company). ISBN 0-7167-1946-0.</ref>
 
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|-
 
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| '''[[Ginkgophyta]]'''
 
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| align="left" | ginkgo
 
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| align="right" | 1 <ref>Taylor, Thomas N. & Edith L. Taylor, 1993. ''The Biology and Evolution of Fossil Plants'', page 636. (New Jersey: Prentice-Hall). ISBN 0-13-651589-4.</ref>
 
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|-
 
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| '''[[Pinophyta]]'''
 
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| align="left" | conifers
 
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| align="right" | 630 <ref name="Raven 2005" />
 
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|-
 
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| '''[[Gnetophyta]]'''
 
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| align="left" | gnetophytes
 
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| align="right" | 70 <ref name="Raven 2005" />
 
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|-
 
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| '''[[Flowering plant|Magnoliophyta]]'''
 
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| align="left" | flowering plants
 
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| align="right" | 258,650 <ref>lnternational Union for Conservation of Nature and Natural Resources, 2006. ''[http://www.iucnredlist.org/ IUCN Red List of Threatened Species:Summary Statistics]''</ref>
 
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|}
 
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{{-}}
 
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===Phylogeny===
 
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A proposed phylogeny of the 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>Smith, Alan R., Kathleen M. Pryer, E. Schuettpelz, P. Korall, H. Schneider, & Paul G. Wolf. (2006). "[http://www.pryerlab.net/publication/fichier749.pdf A classification for extant ferns]". ''Taxon'' 55(3): 705-731.</ref> The [[Prasinophyceae]] may be a paraphyletic basal group to all green plants.
 
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{{clade| style=font-size:75%;line-height:75%
 
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|1={{clade
 
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|1=[[Prasinophyceae]] (micromonads)
 
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|2={{clade
 
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|label1=Streptobionta
 
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|1={{clade
 
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|1={{clade
 
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|label1=[[Embryophyte]]s
 
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|1={{clade
 
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|1={{clade
 
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|label1=Stomatophytes
 
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|1={{clade
 
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|1={{clade
 
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|label1=Polysporangiates
 
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|1={{clade
 
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|1={{clade
 
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|label1=[[Vascular plant|Tracheophytes]]
 
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|1={{clade
 
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<!-- SECTION move to left; too much indenting -->
 
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|label1=Eutracheophytes
 
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|1={{clade
 
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|label1=Euphyllophytina
 
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|1={{clade
 
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|label1=Lignophytia
 
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|1={{clade
 
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|1='''[[Spermatophyta|Spermatophytes]]''' (seed plants)
 
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|2=[[Progymnospermophyta]]&nbsp;&dagger;
 
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}}
 
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|label2='''[[Fern|Pteridophyta]]'''
 
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|2={{clade
 
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|1={{clade
 
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|1=[[Pteridopsida]] (true ferns)
 
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|2=[[Marattiopsida]]
 
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|3=[[Equisetopsida]] (horsetails)
 
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|4=[[Psilotopsida]] (whisk ferns & adders'-tongues)
 
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|5=[[Cladoxylopsida]]&nbsp;&dagger;
 
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}}
 
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}}
 
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}}
 
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|label2=Lycophytina
 
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|2={{clade
 
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|1='''[[Lycopodiophyta]]'''
 
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|2=[[Zosterophyllophyta]]&nbsp;&dagger;
 
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}}
 
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}}
 
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|2=[[Rhyniophyta]]&nbsp;&dagger;
 
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<!-- END SECTION return to full indenting -->
 
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}}
 
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}}
 
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|2=''[[Aglaophyton]]''&nbsp;&dagger;
 
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|3=[[Horneophytopsida]]&nbsp;&dagger;
 
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}}
 
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}}
 
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|2='''[[Moss|Bryophyta]]''' (mosses)
 
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|3='''[[Anthocerotophyta]]''' (hornworts)
 
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}}
 
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}}
 
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|2='''[[Marchantiophyta]]''' (liverworts)
 
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}}
 
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}}
 
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|2='''[[Charophyta]]'''
 
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}}
 
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}}
 
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|3={{clade
 
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|label1='''[[Chlorophyta]]'''
 
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|1={{clade
 
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|1={{clade
 
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|1=[[Trebouxiophyceae]] (Pleurastrophyceae)
 
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|2=[[Chlorophyceae]]
 
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}}
 
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|2=[[Ulvophyceae]]
 
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}}
 
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}}
 
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}}
 
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}}
 
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===Embryophytes===
 
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{{main|Embryophyte}}
 
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[[Image:Ferns02.jpg|thumb|250px|''[[Dicksonia antarctica]]'', a species of [[tree fern]].]]
 
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Most familiar are the [[multicellular]] land plants, called [[embryophyte]]s. They include the [[vascular plant]]s, plants with full systems of [[leaf|leaves]], [[Plant stem|stems]], and [[root]]s. They also include a few of their close relatives, often called ''[[bryophytes]]'', of which [[moss]]es and [[Marchantiophyta|liverworts]] are the most common.
 
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All of these plants have [[eukaryote|eukaryotic]] cells with [[cell wall]]s composed of [[cellulose]], and most obtain their energy through [[photosynthesis]], using [[light]] and [[carbon dioxide]] to synthesize food. About three hundred plant species do not photosynthesize but are [[parasite]]s on other species of photosynthetic plants. Plants are distinguished from [[green alga]]e, 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.
 
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Bryophytes first appeared during the early [[Palaeozoic]]. They can only survive where moisture is available for significant periods, although some species are desiccation tolerant. Most species of bryophyte 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]]. The sporophyte is short-lived and remains dependent on its parent gametophyte.
 
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Vascular plants first appeared during the [[Silurian]] period, and by the [[Devonian]] had diversified and spread into many different land environments. They have a number of adaptations that allowed them to overcome the limitations of the bryophytes. These include a cuticle resistant to desiccation, and vascular tissues which transport water throughout the organism. In most the sporophyte acts as a separate individual, while the gametophyte remains small.
 
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The first primitive seed plants, Pteridosperms (seed ferns) and Cordaites, both groups now extinct, appeared in the late Devonian and diversified through the Carboniferous, with further evolution through the [[Permian]] and [[Triassic]] periods. In these the gametophyte stage is completely reduced, and the sporophyte begins life inside an enclosure called a [[seed]], which develops while on the parent plant, and with fertilisation by means of [[pollen]] grains. Whereas other vascular plants, such as ferns, reproduce by means of spores and so need moisture to develop, some seed plants can survive and reproduce in extremely arid conditions.
 
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Early seed plants are referred to as gymnosperms (naked seeds), as the seed embryo is not enclosed in a protective structure at pollination, with the pollen landing directly on the embryo. Four surviving groups remain widespread now, particularly the [[conifer]]s, which are dominant [[tree]]s in several [[biome]]s. The angiosperms, comprising the [[flowering plant]]s, were the last major group of plants to appear, emerging from within the gymnosperms during the [[Jurassic]] and diversifying rapidly during the [[Cretaceous]]. These differ in that the seed embryo (angiosperm) is enclosed, so the pollen has to grow a tube to penetrate the protective seed coat; they are the predominant group of flora in most biomes today.
 
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=== Fossils ===
 
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{{Main|Paleobotany|Plant fossil|Evolutionary history of plants}}
 
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[[Image:Petrified_forest_log_1_md.jpg|250px|thumb|A petrified log in [[Petrified Forest National Park]].]]
 
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Plant [[fossil]]s include roots, wood, leaves, seeds, fruit, [[pollen]], [[spores]], [[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 ([[dinoflagellates]] and [[acritarchs]]) 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.
 
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The earliest fossils clearly assignable to Kingdom Plantae are fossil green algae from the [[Cambrian]].  These fossils resemble calcified multicellular members of the [[Dasycladales]].  Earlier [[Precambrian]] fossils are known which resemble single-cell green algae, but definitive identity with that group of algae is uncertain.
 
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The oldest known [[trace fossil]]s of embryophytes date from the [[Ordovician]], though such fossils are fragmentary.  By the [[Silurian]], fossils of whole plants are preserved, including the [[lycophyte]] ''[[Baragwanathia longifolia]]''.  From the Devonian, detailed fossils of [[rhyniophyte]]s have been found. Early fossils of these ancient plants show the individual cells within the plant tissue. The [[Devonian period]] also saw the evolution of what many believe to be the first modern tree, ''[[Archaeopteris]]''. This fern-like tree combined a woody trunk with the fronds of a fern, but produced no seeds.
 
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The [[Coal Measures]] are a major source of [[Palaeozoic]] 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 Forest at Victoria Park in [[Glasgow]], [[Scotland]], the stumps of ''[[Lepidodendron]]'' trees are found in their original growth positions.
 
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The fossilized remains of conifer and angiosperm roots, stems and branches may be locally abundant in lake and inshore sedimentary rocks from the [[Mesozoic]] and [[Caenozoic]] eras. [[Coast Redwood|Sequoia]] and its allies, [[magnolia]], [[oak]], and [[Arecaceae|palms]] are often found.
 
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[[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.
 
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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.
 
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==Life processes==
 
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===Growth===
 
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Most of the solid material in a plant is taken from the atmosphere. Through a process known as [[photosynthesis]], plants use the energy in [[sunlight]] to convert carbon dioxide from the atmosphere into simple [[sugars]]. These sugars are then used as building blocks and form the main structural component of the plant. Plants rely on soil primarily for support and water (in quantitative terms), but also obtain [[nitrogen]], [[phosphorus]] and other crucial elemental nutrients. For the majority of plants to grow successfully they also require oxygen in the atmosphere (for respiration in the dark) and oxygen around their roots. However, a few specialized vascular plants, such as [[Mangrove]]s, can grow with their roots in anoxic conditions.
 
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[[Image:Leaf 1 web.jpg|thumb|right|300px|The [[leaf]] is the primary site of [[photosynthesis]] in plants.]]
 
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==== Factors affecting growth ====
 
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The genotype of a plant affects its growth, for example selected varieties 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>
 
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Growth is also determined by [[environmental]] factors, such as [[temperature]], available [[water]], available [[light]], and available [[nutrients]] in the soil. Any change in the availability of these external conditions will be reflected in the plants growth.
 
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Biotic factors (living organisms) also affect plant growth.
 
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*Plants compete with other plants for space, water, light and nutrients. Plants can be so crowded that no single individual makes normal growth.<ref name=Robbins/>
 
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*Many plants rely on birds and insects to affect pollination.
 
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*Grazing animals may completely affect vegetation.
 
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*Soil fertility is influenced by the activity of bacteria and fungi.
 
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*Bacteria, fungi, viruses, nematodes and insects can parasitise plants.
 
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*Some plant roots require an association with fungi to maintain normal activity (mycorrhizal aasociation).<ref name=Robbins/>
 
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Simple plants like algae may have short life spans as individuals, but their populations are commonly seasonal. Other plants may be organized according to their seasonal growth pattern:
 
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* [[Annual plant|Annual]]: live and reproduce within one growing season.
 
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* [[Biennial plant|Biennial]]: live for two growing seasons; usually reproduce in second year.
 
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* [[Perennial plant|Perennial]]: live for many growing seasons; continue to reproduce once mature.
 
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Among the vascular plants, perennials include both [[evergreen]]s that keep their leaves the entire year, and [[deciduous]] plants which lose their leaves for some part. In [[temperate]] and [[boreal]] climates, they generally lose their leaves during the winter; many [[tropical]] plants lose their leaves during the dry season.
 
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The growth rate of plants is extremely variable. Some mosses grow less than 0.001 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.
 
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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) 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 | quotes=no | journal=Biochemical Journal | year=2005 | volume=388 | issue=Part&nbsp;1 | pages=151 &ndash; 157 |url=http://www.biochemj.org/bj/388/0151/bj3880151.htm | id=PMID 15631617}}</ref>
 
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===Internal distribution===
 
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[[Image:ficusxylem.jpg|thumb|300px|Photographs showing [[xylem]] elements in the shoot of a [[fig]] tree (''Ficus alba''): crushed in [[hydrochloric acid]], between slides and cover slips.]]
 
−
[[Nutrient]]s and water from the soil and the organic compound produces in leaves are distributed to specific areas in the plant through the [[xylem]] and [[phloem]]. The xylem draws water and nutrients up from the roots to the upper sections of the plant's body, and the phloem conducts other materials, such as the [[glucose]] produced during [[photosynthesis]], which gives the plant energy to keep growing and [[seeding]].
 
−
 
 
−
The xylem consists of [[tracheid]]s, which are dead hard-walled cells arranged to form tiny tubes to function in water transport. A tracheid cell wall usually contains the polymer [[lignin]]. The phloem however consists of living cells called [[sieve-tube member]]s. Between the sieve-tube members are sieve plates, which have pores to allow molecules to pass through. Sieve-tube members lack such organs as nuclei or ribosomes, but cells next to them, the companion cells, function to keep the sieve-tube members alive.
 
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−
Movement of nutrients, water, sugars and waste is effected by transpiration, conduction and absorption. 
 
−
 
 
−
==== Transpiration ====
 
−
The most abundant [[compound]] in most plants is [[water]], serving a large role in the various processes taking place. [[Transpiration]] is the main process a plant can call upon to move compounds within its tissues. The basic minerals and nutrients a plant is composed of remain, generally, within the plant. Water, however, is constantly being lost from the plant through its [[metabolic]] and [[photosynthetic]] processes to the atmosphere.
 
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−
Water is transpired from the plants leaves via [[stomata]], carried there via leaf [[veins]] and vascular bundles within the plants [[cambium]] layer. The movement of water out of the leaf stomata creates, when the leaves are considered collectively, a transpiration pull. The pull is created through water [[surface tension]] within the plant cells. The draw of water upwards is assisted by the movement of water into the roots via [[osmosis]]. This process also assists the plant in absorbing nutrients from the soil as soluble [[salts]], a process known as absorption.
 
−
 
 
−
==== Absorption ====
 
−
[[Xylem]] cells move water and nutrient solutions upwards towards other plant [[organs]] from the roots and fine [[root]] hairs. Living roots cells actively absorb water in the absence of transpiration pull via osmosis creating root pressure. There are times when plants do not have transpiration pull, usually due to lack of light or other environmental elements. Water in the plant tissues may move to the roots to assist in passive absorption.
 
−
 
 
−
==== Conduction ====
 
−
[[Xylem]] and [[phloem]] tissues are involved in the conduction processes within plants. The movement of foods throughout the plant takes place mainly in the phloem. Plant conduction (food movement) is from an area of high food content, place of manufacture ([[photosynthesis]]) or storage, to a place of food utilisation, or from a point of manufacture to storage tissues. Mineral salts are translocated in the xylem tissues.<ref name=Robbins />
 
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−
==Ecology==
 
−
{{main|Ecology}}
 
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The [[photosynthesis]] conducted by land plants and algae is the ultimate source of energy and organic material in nearly all ecosystems. Photosynthesis radically changed the composition of the early Earth's 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.
 
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−
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 prevention of [[soil erosion]].
 
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−
===Distribution===
 
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{{section-stub}}
 
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Plants are distributed [[worldwide]] in varying numbers. 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 and [[forest]]s.
 
−
 
 
−
===Ecological relationships===
 
−
[[Image:VFT ne1.JPG|thumb|The [[Venus Flytrap]], a species of [[carnivorous plant]].]]
 
−
Numerous animals have coevolved with plants. Many animals [[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 [[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 [[broomrape]] and [[toothwort]] that acquire all their nutrients through connections to the roots of other plants, so have no chlorophyll. Some plants, known as [[myco-heterotrophs]], parasitize mycorrhizal fungi, and hence act as [[epiparasites]] on other plants.
 
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−
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. Many [[orchid]]s, [[bromeliad]]s, [[fern]]s and [[moss]]es often grow as epiphytes. Bromeliad epiphytes accumulate water in leaf axils to form phytotelmata, complex aquatic food webs.<ref>Bromeliad Phytotelmata[http://bromeliadbiota.ifas.ufl.edu/bromfit.htm]</ref>
 
−
 
 
−
A few plants are [[carnivorous plant|carnivorous]], such as the [[Venus Flytrap]] and [[sundew]]. They trap small animals and digest them to obtain mineral nutrients, especially nitrogen.
 
−
 
 
−
==Importance==
 
−
[[Image:Potato plant.jpg|thumb|200px|[[Potato]] plant. Potatoes spread to the rest of the world after European contact with the Americas in the late 1400s and early 1500s and have since become an important field [[crop]].]]
 
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[[Image:Timber_DonnellyMills2005_SeanMcClean.jpg|thumb|200px|right|[[Timber]] in storage for later processing at a [[sawmill]].]]
 
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[[Image:Taxus wood.jpg|200px|thumb|A section of a [[Taxus|Yew]] branch showing 27 annual growth rings, pale sapwood and dark heartwood, and [[pith]] (centre dark spot). The dark radial lines are small knots.]]
 
−
The study of plant uses by people is termed economic botany or [[ethnobotany]]. They are often used as synonyms but some consider economic botany to focus mainly on uses of modern cultivated plants, while ethnobotany studies uses of indigenous plants by native peoples. Human cultivation of plants is part of [[agriculture]], which is the basis of human civilization. Plant agriculture is subdivided into [[agronomy]], [[horticulture]] and [[forestry]].
 
−
 
 
−
===Food===
 
−
Virtually all human nutrition depends on land plants directly or indirectly. Much of human nutrition depends on [[cereals]], especially [[maize|maize or corn]], [[wheat]] and [[rice]] or other [[staple crop]]s such as [[potato]], [[cassava]], and [[legume]]s. Other parts from plants that are eaten include [[fruits]], [[vegetables]], [[nut (fruit)|nuts]], [[herbs]], [[spices]] and [[flowers|edible flowers]]. Beverages from plants include [[coffee]], [[tea]], [[wine]], [[beer]] and [[alcohol]]. [[Sugar]] is obtained mainly from [[sugar cane]] and [[sugar beet]]. [[Cooking oil]]s and [[margarine]] come from corn, [[soybean]], [[canola]], [[safflower]], [[sunflower]], [[olive]] and others. [[Food additives]] include [[gum arabic]], [[guar gum]], [[locust bean gum]], [[starch]] and [[pectin]].
 
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−
===Nonfood products===
 
−
[[Wood]] is used for buildings, furniture, paper, cardboard, musical instruments and sports equipment. Cloth is often made from [[cotton]], [[flax]] or synthetic fibers derived from [[cellulose]], such as [[rayon]] and [[acetate]]. Renewable fuels from plants include [[firewood]], [[peat]] and many other [[biofuel]]s. [[Coal]] and [[petroleum]] are fossil fuels derived from plants. Medicines derived from plants include [[aspirin]], [[taxol]], [[morphine]], [[quinine]], [[reserpine]], [[colchicine]], [[digitalis]] and [[vincristine]]. There are hundreds of herbal supplements such as [[ginkgo]], [[Echinacea]], [[feverfew]], and [[Saint John's wort]]. [[Pesticides]] derived from plants include [[nicotine]], [[rotenone]], [[strychnine]] and [[pyrethrin]]s. Drugs obtained from plants include [[opium]], [[cocaine]] and [[cannabis (drug)|marijuana]]. Poisons from plants include [[ricin]], [[Conium|hemlock]] and [[curare]]. Plants are the source of many natural products such as fibers, essential oils, dyes, pigments, waxes, tannins, latex, gums, resins, alkaloids, amber and cork. Products derived from plants include soaps, paints, shampoos, perfumes, cosmetics, turpentine, rubber, varnish, lubricants, linoleum, plastics, inks, chewing gum and hemp rope. Plants are also a primary source of basic [[chemicals]] for the industrial synthesis of a vast array of organic chemicals. These chemicals are used in a vast variety of studies and experiments.
 
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−
===Aesthetic uses===
 
−
Thousands of plant species are cultivated to beautify the human environment as well as to provide shade, modify temperatures, reduce windspeed, abate noise, provide privacy and prevent soil erosion. People use cut flowers, dried flowers and house plants indoors. Outdoors, they use lawngrasses, shade trees, ornamental trees, shrubs, vines, herbaceous perennials and bedding plants. Images of plants are often used in art, architecture, humor, [[Language of flowers|language]] and photography and on textiles, money, stamps, flags and coats of arms. Living plant art forms include [[topiary]], [[bonsai]], [[ikebana]] and [[espalier]]. [[Ornamental plant]]s have sometimes changed the course of history, as in [[tulipomania]]. Plants are the basis of a multi-billion dollar per year tourism industry which includes travel to [[arboretum]]s, [[botanical garden]]s, [[garden tourism|historic gardens]], [[national park]]s, [[tulip festival]]s, [[rainforests]], [[forest]]s with colorful autumn leaves and the [[National Cherry Blossom Festival]]. Venus flytrap, [[sensitive plant]] and [[resurrection plant]] are examples of plants sold as novelties.
 
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−
===Scientific and cultural uses===
 
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[[Tree rings]] are an important method of dating in archeology and serve as a record of past climates. Basic biological research has often been done with plants, such as the pea plants used to derive [[Gregor Mendel]]'s laws of genetics. Space stations or space colonies may one day rely on plants for [[Controlled Ecological Life Support System|life support]]. Plants are used as [[National emblem|national]] and state emblems, including [[List of U.S. state trees|state trees]] and [[state flowers]]. Ancient trees are revered and many are [[List of famous trees|famous]]. Numerous world records are held by plants. Plants are often used as memorials, gifts and to mark special occasions such as births, deaths, weddings and holidays. Plants figure prominently in [[Trees in mythology|mythology]], religion and [[List of fictional plants|literature]]. The field of [[ethnobotany]] studies plant use by indigenous cultures which helps to conserve endangered species as well as discover new [[herbalism|medicinal plants]]. [[Gardening]] is the most popular leisure activity in the U.S. Working with plants or [[horticulture therapy]] is beneficial for rehabilitating people with disabilities.  Certain plants contain psychotropic chemicals which are extracted and ingested, including [[tobacco]], [[Cannabis (drug)|cannabis]] (marijuana), and [[opium]].
 
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−
===Negative effects===
 
−
[[Weed]]s are plants that grow where people do not want them. 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. Invasive plants cause billions of dollars in crop losses annually by displacing crop plants, they increase the cost of production and the use of chemical means to control them effects the environment.
 
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Plants may cause harm to people. Plants that produce windblown pollen invoke allergic reactions in people who suffer from [[hay fever]]. A wide variety of plants are [[List of poisonous plants|poisonous]]. 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 tobacco, cannabis (marijuana), [[cocaine]] and [[opium]], causing damage to health or even death.<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 have negative effects on the economy, effecting worker productivity and law enforcement costs.<ref>{{ cite web |url=http://www.whitehousedrugpolicy.gov/NEWS/press02/012302.html |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 in people and animals when ingested, while other plants cause food intolerances that negatively effect health.
 
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−
==See also==
 
−
* [[Biosphere]]
 
−
* [[Botany]]
 
−
* [[Evolutionary history of plants]]
 
−
* [[Flower]]
 
−
* [[Forest]]
 
−
* [[Fruit]]
 
−
* [[Garden]]
 
−
* [[Gardening]]
 
−
* [[Greenhouse]]
 
−
* [[Houseplant]]
 
−
* [[List of poisonous plants]]
 
−
* [[Photosynthesis]]
 
−
* [[Plant cell]]
 
−
* [[Plant defense against herbivory]]
 
−
* [[Plant fossil]]s
 
−
* [[Plant perception (paranormal)]]
 
−
* [[Plant perception (physiology)]]
 
−
* [[Rapid plant movement]]
 
−
* [[Tree]]
 
−
* [[Vegetable]]
 
−
* [[Vegetation]]
 
−
* [[Phytopathology]]
 
−
 
 
−
== References ==
 
−
{{reflist}}
 
−
 
 
−
===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.
 
−
* Trewavas, A. (2003). [http://aob.oxfordjournals.org/cgi/content/full/92/1/1 Aspects of Plant Intelligence], ''Annals of Botany'' 92: 1-20.
 
−
 
 
−
;Species estimates and counts:
 
−
* Prance, G. T. (2001). Discovering the Plant World. ''Taxon'' 50: 345-359.
 
−
* International Union for Conservation of Nature and Natural Resources (IUCN) Species Survival Commission (2004). IUCN Red List of Threatened Species [http://www.redlist.org].
 
−
* Both the above are cited in ''Nature Conservancy'', Spring 2006, p. 14.
 
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==External links==
 
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{{Portalpar|Biology}}
 
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{{sisterlinks|Plant}}
 
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{{Wikispecies|Plantae}}
 
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{{Wikibookspar|Dichotomous Key|Plantae}}
 
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* [http://tolweb.org/Green_plants Tree of Life]
 
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* [http://www.scribd.com/doc/20674/Prodigeus-plants/ Answers to several questions from curious kids about plants]
 
−
* {{cite journal | quotes=no|author=Chaw, S.-M. et al.|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=Molec. Biol. Evol.|volume=14|issue=1|pages=56-68|year=1997}}
 
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* [http://florabase.calm.wa.gov.au/phylogeny/cronq88.html Interactive Cronquist classification]
 
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* [http://www.pflanzenliebe.de Plant Picture Gallery]
 
−
* [http://www.alpine-plants-jp.com/art/index_photo2b.htm Plant Photo Gallery of Japan] - Flavon's Wild herb and Alpine plants
 
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* [http://www.prota.org/uk/About+Prota/ Plant Resources of Tropical Africa]
 
−
* [http://database.prota.org/search.htm PROTAbase]
 
−
* [http://ucjeps.berkeley.edu/INA.html Index Nominum Algarum]
 
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−
===Botanical and vegetation databases===
 
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* [http://www.efloras.org/index.aspx e-Floras (Flora of China, Flora of North America and others)]
 
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* [http://davesgarden.com/pf/ PlantFiles - 150,000 plants]
 
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* [http://www.anbg.gov.au/cpbr/databases/ Australia]
 
−
* [http://www.chilebosque.cl Chilean plants at ''Chilebosque'']
 
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* [http://rbg-web2.rbge.org.uk/FE/fe.html Flora Europaea]
 
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* [http://www.floraweb.de FloraWeb - Flora of Central Europe]
 
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* [http://www.efloras.org/flora_page.aspx?flora_id=1 Flora of North America]
 
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* [http://wildflower.utexas.edu/ Native Plant Information Network]
 
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* [http://plants.usda.gov/ United States Department of Agriculture]
 
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* [http://www.alpine-plants-jp.com/botanical_name/list_of_japanese_wild_plants_abelia_buxus.htm List of Japanese Wild Plants Online]
 
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* [http://www.ntbg.org/plants/choose_a_plant.php Meet the Plants-National Tropical Botanical Garden]
 
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{{-}}
 
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{{Botany}}
 
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{{Nature nav}}
 
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[[Category:Plants| ]]
 
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[[Category:Plant taxonomy]]
 

Revision as of 04:28, 30 October 2008

Plants
Plants diversity.jpg
Plant Info
Scientific classification
Domain: Eukaryota
Kingdom: Plantae
Haeckel, 1866

Divisions
Green algae

Land plants (embryophytes)

Plants are one of the five kingdoms used to classify all life. The plant kingdom, known as Plantae is divided into progressively smaller subgroups, usually based on their family tree. The primary division is between vascular and non-vascular plants - with the vascular plants being of most interest to gardeners.

Non-vascular versus vascular

Plants that bear seed

Lifespan

Plant classification and nomenclature

Species, hybrids and cultivars

Monocots and dicots

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