Editing Embryophyte (section)

==Diversity==

===Non-vascular land plants===
{{further|Alternation of generations}}

[[File:Barbula spadicea (Sporenkapseln) IMG 0434.JPG|thumb|Bryophytes, such as these mosses, produce unbranched, stalked sporophytes from which their spores are released.]]

The non-vascular land plants, namely the [[moss]]es (Bryophyta), [[hornwort]]s (Anthocerotophyta), and [[liverwort]]s (Marchantiophyta), are relatively small plants, often confined to environments that are humid or at least seasonally moist. They are limited by their reliance on water needed to disperse their [[gamete]]s; a few are truly aquatic. Most are tropical, but there are many arctic species. They may locally dominate the ground cover in [[tundra]] and [[Arctic–alpine]] habitats or the epiphyte flora in rain forest habitats.

They are usually studied together because of their many similarities. All three groups share a [[haploid]]-dominant ([[gametophyte]]) life cycle and unbranched [[sporophyte]]s (the plant's [[diploid]] [[Alternation of generations|generation]]). These traits appear to be common to all early diverging lineages of non-vascular plants on the land. Their life-cycle is strongly dominated by the haploid gametophyte generation. The sporophyte remains small and dependent on the parent gametophyte for its entire brief life. All other living groups of land plants have a life cycle dominated by the diploid sporophyte generation. It is in the diploid sporophyte that vascular tissue develops. In some ways, the term "non-vascular" is a misnomer. Some mosses and liverworts do produce a special type of vascular tissue composed of complex water-conducting cells.<ref name="Brodribb-2020">{{Cite journal |last=Brodribb |first=T. J. |last2=Carriquí |first2=M. |last3=Delzon |first3=S. |last4=McAdam |first4=S. A. M. |last5=Holbrook |first5=N. M. |date=2020-03-09 |title=Advanced vascular function discovered in a widespread moss |url=https://www.nature.com/articles/s41477-020-0602-x |journal=Nature Plants |language=en |volume=6 |issue=3 |pages=273–279 |doi=10.1038/s41477-020-0602-x |issn=2055-0278|url-access=subscription }}</ref> However, this tissue differs from that of "vascular" plants in that these water-conducting cells are not lignified.<ref>{{Cite journal |last=Renault |first=Hugues |last2=Alber |first2=Annette |last3=Horst |first3=Nelly A. |last4=Basilio Lopes |first4=Alexandra |last5=Fich |first5=Eric A. |last6=Kriegshauser |first6=Lucie |last7=Wiedemann |first7=Gertrud |last8=Ullmann |first8=Pascaline |last9=Herrgott |first9=Laurence |last10=Erhardt |first10=Mathieu |last11=Pineau |first11=Emmanuelle |last12=Ehlting |first12=Jürgen |last13=Schmitt |first13=Martine |last14=Rose |first14=Jocelyn K. C. |last15=Reski |first15=Ralf |date=2017-03-08 |title=A phenol-enriched cuticle is ancestral to lignin evolution in land plants |url=https://www.nature.com/articles/ncomms14713 |journal=Nature Communications |language=en |volume=8 |issue=1 |doi=10.1038/ncomms14713 |issn=2041-1723 |pmc=5344971 |pmid=28270693}}</ref> It is unlikely that the water-conducting cells in mosses are homologous with the vascular tissue in "vascular" plants.<ref name="Brodribb-2020" /> 

Like the vascular plants, they have differentiated stems, and although these are most often no more than a few centimeters tall, they provide mechanical support. Most have leaves, although these typically are one cell thick and lack veins. They lack true roots or any deep anchoring structures. Some species grow a filamentous network of horizontal stems, but these have a primary function of mechanical attachment rather than extraction of soil nutrients (Palaeos 2008).

===Rise of vascular plants===
[[Image:Rhynia reconstruction.svg|thumb|upright=0.5|Reconstruction of a plant of ''Rhynia'']]
During the [[Silurian]] and [[Devonian]] periods (around {{period span/brief|Silurian|Devonian|-1}}), plants evolved which possessed true vascular tissue, including cells with walls strengthened by lignin ([[tracheid]]s). Some extinct early plants appear to be between the grade of organization of bryophytes and that of true vascular plants (eutracheophytes). Genera such as ''[[Horneophyton]]'' have water-conducting tissue more like that of mosses, but a different life-cycle in which the sporophyte is branched and more developed than the gametophyte. Genera such as ''[[Rhynia]]'' have a similar life-cycle but have simple tracheids and so are a kind of vascular plant.<ref>{{Cite journal |last=Kidston |first=R. |last2=Lang |first2=W. H. |date=January 1996 |title=XXIV.—On Old Red Sandstone Plants showing Structure, from the Rhynie Chert Bed, Aberdeenshire. Part I. Rhynia Gwynne-Vaughani, Kidston and Lang |url=https://www.cambridge.org/core/product/identifier/S0263593300006805/type/journal_article |journal=Transactions of the Royal Society of Edinburgh: Earth Sciences |language=en |volume=87 |issue=3 |pages=427–450 |doi=10.1017/S0263593300006805 |issn=0263-5933|url-access=subscription }}</ref> It was assumed that the gametophyte dominant phase seen in bryophytes used to be the ancestral condition in terrestrial plants, and that the sporophyte dominant stage in vascular plants was a derived trait. However, the gametophyte and sporophyte stages were probably equally independent from each other, and that the mosses and vascular plants in that case are both derived, and have evolved in opposite directions.<ref>{{Cite journal|title=Sporophytes of polysporangiate land plants from the early Silurian period may have been photosynthetically autonomous|first1=Petr|last1=Štorch|first2=Viktor|last2=Žárský|first3=Jiří|last3=Bek|first4=Jiří|last4=Kvaček|first5=Milan|last5=Libertín|date=May 28, 2018|journal=Nature Plants|volume=4|issue=5|pages=269–271|doi=10.1038/s41477-018-0140-y|pmid=29725100|s2cid=19151297}}</ref>

During the Devonian period, vascular plants diversified and spread to many different land environments. In addition to vascular tissues which transport water throughout the body, tracheophytes have an outer layer or cuticle that resists [[desiccation|drying out]]. The sporophyte is the dominant generation, and in modern species develops [[leaf|leaves]], [[Plant stem|stems]] and [[root]]s, while the gametophyte remains very small.

{{Further|Polysporangiophyte|Horneophytopsida|Rhyniopsida}}
{{Clear}}

===Lycophytes and euphyllophytes===
[[File:Lycopodiella inundata 002.jpg|thumb|''Lycopodiella inundata'', a lycophyte]]
{{Main|Lycopodiophyta}}
All the vascular plants which disperse through spores were once thought to be related (and were often grouped as 'ferns and allies'). However, recent research suggests that leaves evolved quite separately in two different lineages. The lycophytes or lycopodiophytes – modern clubmosses, spikemosses and quillworts – make up less than 1% of living vascular plants. They have small leaves, often called 'microphylls' or 'lycophylls', which are borne all along the stems in the clubmosses and spikemosses, and which effectively grow from the base, via an intercalary [[meristem]].<ref name="Pryer-2004">{{Citation |last1=Pryer |first1=K.M. |last2=Schuettpelz |first2=E. |last3=Wolf |first3=P.G. |last4=Schneider |first4=H. |last5=Smith |first5=A.R. |last6=Cranfill |first6=R. |name-list-style=amp |year=2004 |title=Phylogeny and evolution of ferns (monilophytes) with a focus on the early leptosporangiate divergences |journal=American Journal of Botany |volume=91 |issue=10 |pages=1582–98 |doi=10.3732/ajb.91.10.1582 |pmid=21652310 }}, pp. 1582–3</ref> It is believed that microphylls evolved from outgrowths on stems, such as spines, which later acquired veins (vascular traces).<ref>{{Citation |last=Boyce |first=C.K. |year=2005 |editor-last=Holbrook |editor-first=N.M. |editor2-last=Zwieniecki |editor2-first=M.A. |contribution=The evolutionary history of roots and leaves |title=Vascular Transport in Plants |location=Burlington |publisher=Academic Press |isbn=978-0-12-088457-5 |name-list-style=amp|doi=10.1016/B978-012088457-5/50025-3 |pages=479–499}}</ref>

Although the living lycophytes are all relatively small and inconspicuous plants, more common in the moist tropics than in temperate regions, during the [[Carboniferous]] period tree-like lycophytes (such as ''[[Lepidodendron]]'') formed huge forests that dominated the landscape.<ref>{{citation |doi=10.1130/G31182.1 |last1=Sahney |first1=S.|last2=Benton |first2=M.J. |last3=Falcon-Lang |first3=H.J. |year=2010 |title= Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica |journal=Geology |volume= 38 |pages= 1079–1082 |name-list-style=amp|issue=12 |bibcode = 2010Geo....38.1079S }}</ref>

The euphyllophytes, making up more than 99% of living vascular plant species, have large 'true' leaves (megaphylls), which effectively grow from the sides or the apex, via marginal or apical meristems.<ref name="Pryer-2004"/> One theory is that megaphylls evolved from three-dimensional branching systems by first '{{Not a typo|planation}}' – flattening to produce a two dimensional branched structure – and then 'webbing' – tissue growing out between the flattened branches.<ref>{{Citation |last1=Beerling |first1=D.J. |author-link = David Beerling|last2=Fleming |first2=A.J. |year=2007 |title=Zimmermann's telome theory of megaphyll leaf evolution: a molecular and cellular critique |journal=Current Opinion in Plant Biology |volume=10 |issue=1 |pages=4–12 |doi=10.1016/j.pbi.2006.11.006 |name-list-style=amp|pmid=17141552 |bibcode=2007COPB...10....4B }}</ref> Others have questioned whether megaphylls evolved in the same way in different groups.<ref>{{Citation |last=Tomescu |first=A. |year=2009 |title=Megaphylls, microphylls and the evolution of leaf development |journal=Trends in Plant Science |volume=14 |issue=1 |pages=5–12 |doi=10.1016/j.tplants.2008.10.008 |pmid=19070531 }}</ref>{{Clear}}

===Ferns and horsetails===
{{main|Fern}}
The ferns and horsetails (the Polypodiophyta) form a clade; they use spores as their main method of dispersal. Traditionally, whisk ferns and horsetails were historically treated as distinct from 'true' ferns.<ref name="Smith-2006">{{cite journal |last1=Smith |first1=A.R. |last2=Pryer |first2=K.M. |last3=Schuettpelz |first3=E. |last4=Korall |first4=P. |last5=Schneider |first5=H. |last6=Wolf |first6=P.G. |year=2006 |title=A classification for extant ferns |journal=Taxon |volume=55 |issue=3 |pages=705–731 |url=http://www.pryerlab.net/publication/fichier749.pdf |access-date=2011-01-28 |doi=10.2307/25065646 |name-list-style=amp|url-status=dead |archive-url=https://web.archive.org/web/20080226232147/http://www.pryerlab.net/publication/fichier749.pdf |archive-date=2008-02-26 |jstor=25065646 }}</ref> Living whisk ferns and horsetails do not have the large leaves (megaphylls) which would be expected of euphyllophytes. This has probably resulted from reduction, as evidenced by early fossil horsetails, in which the leaves are broad with branching veins.<ref name="Rutishauser-1999">{{cite journal |last=Rutishauser |first=R. |year=1999 |title=Polymerous Leaf Whorls in Vascular Plants: Developmental Morphology and Fuzziness of Organ Identities |journal=International Journal of Plant Sciences |volume=160 |issue=6 |pages=81–103 |doi=10.1086/314221 |pmid=10572024|s2cid=4658142 }}</ref>

Ferns are a large and diverse group, with some 12,000 [[species]].<ref name="Chapman-2009">{{cite web |last=Chapman |first=Arthur D. |year=2009 |title=Numbers of Living Species in Australia and the World. Report for the Australian Biological Resources Study |location=Canberra, Australia |url=http://www.environment.gov.au/biodiversity/abrs/publications/other/species-numbers/index.html |access-date=2011-03-11 }}</ref> A stereotypical fern has broad, much divided leaves, which grow by unrolling.

===Seed plants===
{{main|Spermatophyte}}

[[File:Autumn Conker - geograph.org.uk - 370125.jpg|thumb|Large seed of [[Aesculus|horse chestnut]], ''Aesculus hippocastanum'']]

Seed plants, which first appeared in the fossil record towards the end of the [[Paleozoic]] era, reproduce using [[desiccation]]-resistant capsules called [[seed]]s. Starting from a plant which disperses by spores, highly complex changes are needed to produce seeds. The sporophyte has two kinds of spore-forming organs or sporangia. One kind, the megasporangium, produces only a single large spore, a megaspore. This sporangium is surrounded by sheathing layers or integuments which form the seed coat. Within the seed coat, the megaspore develops into a tiny gametophyte, which in turn produces one or more egg cells. Before fertilization, the sporangium and its contents plus its coat is called an ovule; after fertilization a seed. In parallel to these developments, the other kind of sporangium, the microsporangium, produces microspores. A tiny gametophyte develops inside the wall of a microspore, producing a [[pollen]] grain. Pollen grains can be physically transferred between plants by the [[wind]] or animals, most commonly [[insect]]s. Pollen grains can also transfer to an ovule of the same plant, either with the same flower or between two flowers of the same plant ([[self-fertilization]]). When a pollen grain reaches an ovule, it enters via a microscopic gap in the coat, the micropyle. The tiny gametophyte inside the pollen grain then produces sperm cells which move to the egg cell and fertilize it.<ref>{{Citation |last1=Taylor |first1=T.N. |last2=Taylor |first2=E.L. |last3=Krings |first3=M. |year=2009 |title=Paleobotany, The Biology and Evolution of Fossil Plants |edition=2nd |location=Amsterdam; Boston |publisher=Academic Press |isbn=978-0-12-373972-8 |pages=508ff}}</ref> Seed plants include two clades with living members, the [[gymnosperm]]s and the [[angiosperm]]s or flowering plants. In gymnosperms, the ovules or seeds are not further enclosed. In angiosperms, they are enclosed within the carpel. Angiosperms typically also have other, secondary structures, such as [[petals]], which together form a [[flower]].

[[Meiosis]] in sexual land plants provides a direct mechanism for [[DNA repair|repairing DNA]] in reproductive tissues.<ref name="Hörandl-2024">Hörandl E. Apomixis and the paradox of sex in plants. Ann Bot. 2024 Mar 18:mcae044. doi: 10.1093/aob/mcae044. Epub ahead of print. PMID 38497809</ref> [[Sexual reproduction]] appears to be needed for maintaining long-term [[genome|genomic]] integrity and only infrequent combinations of extrinsic and intrinsic factors allow for shifts to asexuality.<ref name="Hörandl-2024"/>