View source for Lycophyte

{{Short description|Broadly circumscribed group of spore bearing plants}}
{{About|a broadly defined group of plants that includes the extinct zosterophylls|the group excluding the zosterophylls|Lycopodiopsida}}
{{Automatic taxobox
| fossil_range = {{fossil range|428|0}}[[Silurian]]<ref name=KenrCran97>{{cite book | last1=Kenrick | first1=Paul | last2=Crane | first2=Peter R. | year=1997 | title=The Origin and Early Diversification of Land Plants: A Cladistic Study | location=Washington, D. C. | publisher=Smithsonian Institution Press | isbn=978-1-56098-730-7 | pages =339–340 }}</ref> to recent
| image = Lepidodendron reconstrucción.jpg
| image_caption = Reconstruction of a ''[[Lepidodendron]]'' plant
| taxon = Lycophytes
| subdivision_ranks = Classes
| subdivision = 
*[[Lycopodiopsida]] - clubmosses, spikemosses, quillworts, scale trees
*†[[Zosterophyll|Zosterophyllopsida]] - zosterophylls
}}

The '''lycophytes''', when broadly [[Circumscription (taxonomy)|circumscribed]], are a [[vascular plant]] (tracheophyte) subgroup of the kingdom [[Plant]]ae. They are sometimes placed in a division '''Lycopodiophyta''' or '''Lycophyta''' or in a subdivision '''Lycopodiophytina'''. They are one of the oldest lineages of [[Extant taxon|extant]] (living) vascular plants; the group contains extinct plants that have been dated from the [[Silurian]] (ca. 425 million years ago).<ref>{{cite journal|last1=Rickards|first1=R.B.|title=The age of the earliest club mosses: the Silurian Baragwanathia flora in Victoria, Australia|journal=Geological Magazine|date=2000|volume=137|issue=2|pages=207–209|doi=10.1017/s0016756800003800|bibcode=2000GeoM..137..207R}}</ref><ref name="isbn0-19-850065-3">{{cite book |author1=McElwain, Jenny C. |author2=Willis, K. G. |author3=Willis, Kathy |author4=McElwain, J. C. | title = The evolution of plants | publisher = Oxford University Press | location = Oxford [Oxfordshire] | year = 2002 | isbn = 978-0-19-850065-0 }}</ref> Lycophytes were some of the dominating plant species of the [[Carboniferous]] period, and included tree-like species, although extant lycophytes are relatively small plants.<ref>{{Cite book|title=Biology and evolution of ferns and lycophytes|last1=Ranker|first1=T. A.|last2=Hauler|first2=C. H.|publisher=Cambridge University Press|year=2008|location=Cambridge}}</ref>

The scientific names and the informal English names used for this group of plants are ambiguous. For example, "Lycopodiophyta" and the shorter "Lycophyta" as well as the informal "lycophyte" may be used to include the extinct [[zosterophyll]]s or to exclude them.

==Description==
Lycophytes reproduce by [[spore]]s and have [[alternation of generations]] in which (like other vascular plants) the [[sporophyte]] generation is dominant. Some lycophytes are [[Spore#homosporous|homosporous]] while others are [[Spore#heterosporous|heterosporous]].<ref name="Eichhorn">Eichhorn, Evert, and Raven (2005). ''Biology of Plants'', Seventh Edition. 381-388.</ref> When broadly [[Circumscription (taxonomy)|circumscribed]], the lycophytes represent a line of evolution distinct from that leading to all other [[vascular plant]]s, the [[euphyllophyte]]s, such as [[fern]]s, [[gymnosperm]]s and [[flowering plant]]s. They are defined by two [[Synapomorphy and apomorphy|synapomorphies]]: lateral rather than terminal [[Sporangium|sporangia]] (often kidney-shaped or reniform), and [[Xylem#Development|exarch]] [[protostele]]s, in which the protoxylem is outside the metaxylem rather than vice versa. The extinct [[zosterophylls]] have at most only flap-like extensions of the stem ("enations") rather than leaves, whereas extant lycophyte species have [[microphyll]]s, leaves that have only a single vascular trace (vein), rather than the much more complex [[megaphyll]]s of other vascular plants. The extinct genus ''[[Asteroxylon]]'' represents a transition between these two groups: it has a vascular trace leaving the central protostele, but this extends only to the base of the enation.<ref name=Maus14/> See {{section link||Evolution of microphylls}}.

Zosterophylls and extant lycophytes are all relatively small plants, but some extinct species, such as the [[Lepidodendrales]], were tree-like, and formed extensive forests that dominated the landscape and contributed to the formation of [[coal]].<ref name=Maus14/>

==Taxonomy==
===Classification===
In the broadest  [[Circumscription (taxonomy)|circumscription]] of the lycophytes, the group includes the extinct [[zosterophyll]]s as well as the extant (living) lycophytes and their closest extinct relatives. The names and ranks used for this group vary considerably. Some sources use the names "Lycopodiophyta" or the shorter "Lycophyta" to include zosterophylls as well as extant lycophytes and their closest extinct relatives,<ref name=Dowe17>{{Citation |mode=cs1 |last1=Doweld |first1=Alexander B. |date=2017 |title=(2499) Proposal to conserve the name Zosterophyllaceae against Sciadophytaceae (Fossil Lycopodiophyta: Zosterophyllopsida) |journal=Taxon |volume=66 |issue=1 |pages=207–208 |doi=10.12705/661.27 |doi-access=free }}</ref> while others use these names to exclude zosterophylls.<ref name=TaylTaylKrin09/><ref name=Maus14/> The name "Lycopodiophytina" has also been used in the inclusive sense.<ref name=KenrCran97a/><ref name=KenrCran97b/> English names, such as "lycophyte", "lycopodiophyte" or "lycopod", are similarly ambiguous, and may refer to the broadly defined group or only to the extant lycophytes and their closest extinct relatives.

The consensus classification produced by the [[Pteridophyte Phylogeny Group]] classification in 2016 (PPG&nbsp;I) places all extant (living) lycophytes in the class [[Lycopodiopsida]].<ref name=PPGI/> There are around 1,290 to 1,340 such species.<ref name=CallCook99/><ref name=ChriByng16/><ref name=PPGI/> For more information on the classification of extant lycophytes, see {{section link|Lycopodiopsida|Classification}}.

===Phylogeny===
A major [[cladistics|cladistic]] study of land plants was published in 1997 by Kenrick and Crane.<ref name=KenrCran97/> In 2004, Crane et al. published some simplified [[cladogram]]s, based on a number of figures in Kenrick and Crane (1997). Their cladogram for the lycophytes is reproduced below (with some branches collapsed into 'basal groups' to reduce the size of the diagram).<ref name=CranHereFrii04>{{Citation |mode=cs1 |last1=Crane |first1=P.R. |last2=Herendeen |first2=P. |last3=Friis |first3=E.M. |date=2004 |title=Fossils and plant phylogeny |journal=American Journal of Botany |volume=91 |issue=10 |pages=1683–1699 |doi=10.3732/ajb.91.10.1683 |pmid=21652317 |s2cid=8493380 |name-list-style=amp |url=https://semanticscholar.org/paper/a4b2ece71a27bea51259bf2609a788e2436add0d |doi-access=free }}</ref>
{{clade
|1={{Clade panlycophyte|lycophyte-label=lycophytes}}
}}
In this view, the "zosterophylls" comprise a [[Paraphyly|paraphyletic]] group, ranging from forms like ''[[Hicklingia]]'', which had bare stems,<ref name=Edwa76/> to forms like ''[[Sawdonia]]'' and ''[[Nothia]]'', whose stems are covered with unvascularized spines or enations.{{sfnp|Taylor|Taylor|Krings|2009|p=253}}<ref name=KerpHassMosb01/> The genus ''[[Renalia]]'' illustrates the problems in classifying early land plants. It has characteristics both of the non-lycophyte [[rhyniophyte]]s – terminal rather than lateral sporangia – and of the zosterophylls – kidney-shaped sporangia opening along the distal margin.{{sfnp|Taylor|Taylor|Krings|2009|p=250}}

A rather different view is presented in a 2013 analysis by Hao and Xue. Their preferred cladogram shows the zosterophylls and associated genera basal to both the lycopodiopsids and the euphyllophytes, so that there is no clade corresponding to the broadly defined group of lycophytes used by other authors.<ref name=HaoXue13/>
{{Barlabel
|size=6
|at1=3|label1="lycophytes" of other authors|bar1=green
|cladogram=
{{clade|style=line-height:100%
|label1=tracheophytes
|1={{clade
   |state1=double
   |1=basal groups
   |2={{clade
      |1={{clade
         |1=''[[Adoketophyton]]''|barbegin1=green
         |2=Zosterophyllopsida|bar2=green
         }}
      |2={{clade
         |1=Lycopsida|barend1=green
         |2={{clade
            |state1=double
            |1=basal groups (''[[Yunia]]'', ''[[Dibracophyton]]'')
            |2=euphyllophytes
            }}
         }}
      }}
   }}
}}
}}

Some extinct orders of lycophytes fall into the same group as the extant orders. Different sources use varying numbers and names of the extinct orders. The following phylogram shows a likely relationship between some of the proposed Lycopodiopsida orders.{{citation needed|date=October 2019}}
{{clade|style=line-height:100%
|label1=Lycopodiopsida
|1={{clade
   |1={{clade
      |1=[[Lycopodiales]]
      |2=†[[Drepanophycales]]
      }}
   |2={{clade
      |1=[[Selaginellales]]
      |2={{clade
         |1=†[[Lepidodendrales]]
         |2={{clade
            |1=†[[Pleuromeia]]les
            |2=[[Isoetales]]
            }}
         }}
      }}
   }}
}}

==Evolution of microphylls==
[[File:Microphyll evolution omygod.svg|thumb|upright=1.25|Suggested evolution of microphylls: (1) ''[[Sawdonia]]'' (2) ''[[Asteroxylon]]'' (3) ''[[Leclercqia (plant)|Leclercqia]]'']]
Within the broadly defined lycophyte group, species placed in the class [[Lycopodiopsida]] are distinguished from species placed in the [[Zosterophyll|Zosterophyllopsida]] by the possession of [[microphyll]]s. Some zosterophylls, such as the [[Devonian]] ''[[Zosterophyllum|Zosterophyllum myretonianum]]'', had smooth stems (axes). Others, such as ''[[Sawdonia|Sawdonia ornata]]'', had flap-like extensions on the stems ("enations"), but without any vascular tissue. ''[[Asteroxylon]]'', identified as an early lycopodiopsid, had vascular traces that extended to the base of the enations. Species in the genus ''[[Leclercqia (plant)|Leclercqia]]'' had fully vascularized microphylls. These are considered to be stages in the evolution of microphylls.{{sfnp|Taylor|Taylor|Krings|2009|p=267ff}}

==Gallery==
<gallery>
File:Lycopodites.JPG|''Lycopodites'', an early lycopod-like fossil
File:LepidodendronOhio.jpg|External mold of ''[[Lepidodendron]]'' from the [[Upper Carboniferous]] of [[Ohio]].
File:Lycopod bark.jpg|Lycopod bark showing leaf scars, from the Middle Devonian of Wisconsin.
File:Lycopsid joggins mcr1.JPG|Fossil ''in situ'' [[w:lycopsid|lycopsid]], probably [[w:Sigillaria|''Sigillaria'']], with attached [[w:stigmaria|stigmarian roots]].
File:Lycopsid mcr2.jpg|Base of a fossil [[w:lycopsid|lycopsid]] showing connection with [[w:Stigmaria|stigmarian roots]].
File:Zosterophyllum sp. - MUSE cropped.jpg|Reconstruction of a Silurian ''[[Zosterophyllum]]''
File:Nothia.png|Reconstruction of ''[[Nothia|Nothia aphylla]]''
File:Lepidodendron.png|Reconstruction of ''[[Lepidodendron]]''
File:Lycopod axis.jpg|Lycopod axis (branch) from the Middle Devonian of Wisconsin.
File:Lycopodium dendroideum.JPG|''[[Lycopodium dendroideum]]'', a modern member of the [[Lycopodiales]]
File:Closeup of Black-spored Quillwort (Isoetes melanospora).jpg|''[[Isoetes melanospora]]'', a modern member of the [[Isoetales]]
File:Pleuromeia restoration.png|Restoration of ''[[Pleuromeia]]'', an Isoetales genus from the Triassic
</gallery>

== References ==
{{Reflist|refs=
<ref name=CallCook99>{{Citation |mode=cs1 |last1=Callow |first1=R.S. |last2=Cook |first2=Laurence Martin |date=1999 |title=Genetic and evolutionary diversity: the sport of nature |location=Cheltenham |publisher=S. Thornes |isbn=978-0-7487-4336-0 |page=8 |name-list-style=amp }}</ref>

<ref name=ChriByng16>{{Citation |mode=cs1 |last1=Christenhusz, M. J. M. |first1=M.J.M. |last2=Byng |first2=J.W. |date=2016 |title=The number of known plants species in the world and its annual increase |journal=Phytotaxa |volume=261 |issue=3 |pages=201–217 |doi=10.11646/phytotaxa.261.3.1 |name-list-style=amp |doi-access=free }}</ref>

<ref name=Edwa76>{{Citation |mode=cs1 |last1=Edwards |first1=D. |date=1976 |title=The systematic position of ''Hicklingia edwardii'' Kidston and Lang |journal= New Phytologist|volume=76 |pages=173–181 |doi=10.1111/j.1469-8137.1976.tb01449.x |doi-access=free }}</ref>

<ref name=HaoXue13>{{Citation |mode=cs1 |last1=Hao |first1=Shougang |last2=Xue |first2=Jinzhuang |date=2013 |title=The early Devonian Posongchong flora of Yunnan: a contribution to an understanding of the evolution and early diversification of vascular plants |location=Beijing |publisher=Science Press |isbn=978-7-03-036616-0 |at=Fig. 6.8, p. 246 |name-list-style=amp }}</ref>

<ref name=KenrCran97a>{{Citation |mode=cs1 |last1=Kenrick |first1=Paul |last2=Crane |first2=Peter R. |date=1997a |title=The Origin and Early Diversification of Land Plants: A Cladistic Study |location=Washington, D.C. |publisher=Smithsonian Institution Press |isbn=978-1-56098-730-7 |name-list-style=amp }}</ref>

<ref name=KenrCran97b>{{Citation |mode=cs1 |last1=Kenrick |first1=Paul |last2=Crane |first2=Peter R. |date=1997b |title=The origin and early evolution of plants on land |journal=Nature |volume=389 |issue=6646 |pages=33–39 |url=https://www.researchgate.net/publication/242879569 |doi=10.1038/37918 |name-list-style=amp |bibcode=1997Natur.389...33K |s2cid=3866183 }}</ref>

<ref name=KerpHassMosb01>{{Citation |mode=cs1 |last1=Kerp |first1=H. |last2=Hass |first2=M.H. |last3=Mosbrugger |first3=V. |date=2001 |editor1-last=Gensel |editor1-first=P.G. |editor2-last=Edwards |editor2-first=D. |contribution=New Data on ''Nothia aphylla'' Lyon 1964 ex El-Saadawy et Lacey 1979, a Poorly Known Plant from the Lower Devonian Rhynie Chert |title=Plants invade the Land : Evolutionary & Environmental Perspectives |pages=52–82 |location=New York |publisher=Columbia University Press |isbn=978-0-231-11161-4 |name-list-style=amp }}</ref>

<ref name=Maus14>{{Citation |mode=cs1 |last1=Mauseth |first1=James D. |date=2014 |title=Botany : An introduction to Plant Biology |edition=5th |location=Burlington, MA |publisher=Jones & Bartlett Learning |isbn=978-1-4496-6580-7 }}</ref>

<ref name=PPGI>{{Citation |mode=cs1 |author=PPG I |year=2016 |title=A community-derived classification for extant lycophytes and ferns |journal=Journal of Systematics and Evolution |volume=54 |issue=6 |pages=563–603 |doi=10.1111/jse.12229|s2cid=39980610 }}</ref>

<ref name=TaylTaylKrin09>{{Citation |mode=cs1 |last1=Taylor |first1=T.N. |last2=Taylor |first2=E.L. |last3=Krings |first3=M. |date=2009 |title=Paleobotany : The Biology and Evolution of Fossil Plants |edition=2nd |location=Amsterdam; Boston |publisher=Academic Press |isbn=978-0-12-373972-8  |name-list-style=amp  |url={{GBurl|_29tNNeQKeMC}} }}</ref>
}}

==External links==
{{Wikispecies|Lycopodiophyta}}
{{Wikibooks|Dichotomous Key|Lycopodiophyta}}
*[http://www.ucmp.berkeley.edu/IB181/VPL/Lyco/LycoTitle.html Lycophytes]
*[http://www.glasgowmuseums.com/venue/faq.cfm?venueid=2 Fossil Groves]
*[https://web.archive.org/web/20050115164952/http://www.palaeos.com/Plants/Lycophytes/ Paleo Plants]

{{Plant classification|state=collapsed}}
{{Life on Earth}}
{{Taxonbar|from=Q215370}}

[[Category:Lycophytes| ]]
[[Category:Cryptogams]]
[[Category:Plant divisions]]
[[Category:Wenlock first appearances]]
[[Category:Extant Silurian first appearances]]