Editing Lepidodendron (section)

== Description and biology ==

=== Overview ===
[[File:Lepidostrobus variabilis 2.jpg|thumb|''Lepidostrobus'', the [[strobilus]] of ''Lepidodendron'' lycophytes|370x370px]]
[[File:Lepidodendrales reconstrucción 02.jpg|left|thumb|Reconstruction of ''Lepidodendron'' (second from left) compared to a juvenile scale tree (far left) and other [[Lepidodendrales]], which from left to right include ''[[Lepidophloios]], [[Synchysidendron]], [[Diaphorodendron]]'' and ''[[Sigillaria]].'']]
''Lepidodendron'' species were comparable in size to modern trees. The plants had tapering trunks as wide as {{cvt|2|m|ft}} at their base that rose to about {{cvt|40|m}}<ref name="Lopatin">
{{cite book
| isbn = 978-5-903825-14-1
| url         = http://www.ras.ru/paleontological_museum/ae617790-a2fb-43c8-a511-1251c0e32004.aspx?hidetoc=0
| title       = Палеонтологический музей имени Ю.А. Орлова (The Orlov Museum of Paleontology)
| publisher   = Moscow: PIN RAN
| date        = 2012
| access-date  = 2020-10-05
| page        = 56
| author      = A. V. Lopatin
}}</ref> and even {{cvt|50|m}},<ref name="Alekhin">
{{cite book
| url         = https://books.google.com/books?id=OUIPAQAAMAAJ&q=лепидодендроны
| title       = Geografiia rastenii s osnovani botaniki (Geography of plants and basics of botany)
| publisher   = Gos. nauchno-pedagog. izd-vo
| date        = 1961
| access-date  = 2020-10-05
| page        = 167
| author      = V. V. Alekhin
}}</ref> arising from an underground system of horizontally spreading branches that were covered with many rootlets. Though the height of the lycopsids make the plants similar to modern trees, the constant [[Glossary of botanical terms#dichotomous|dichotomy]] of branches created a [[Glossary of plant morphology#Plant habit|habit]] that contrasts with that of modern trees. At the ends of branches were oval-shaped [[strobilus|strobili]] called ''Lepidostrobus'' that had a similar shape to modern cones of a [[spruce]] or [[fir]].<ref name="Students">{{cite book |pages= 93–192 |title= Fossil plants: for students of botany and geology |volume= 1 |url= https://www.biodiversitylibrary.org/item/115734 |publisher= Cambridge University Press |author= Seward, Albert Charles |year= 1898 }}</ref>

=== Stem ===
[[File:PSM V18 D629 Lepidodendron modulatum and diplodigioides.jpg|thumb|upright|Leaf scars shown on a ''Lepidodendron''. The "diamond shape" or scale impressions are common indicators of the leaf scars from ''Lepidodendron'' lycophytes.]]
The stem of the lycopsids had a [[Unifacial cambium|unifacial]] [[Vascular cambium|vascular]] cambium, contrasting with the [[Bifacial cambium|bifacial vascular]] cambium of modern trees. Though the bifacial cambium of modern trees produces both secondary [[phloem]] and [[xylem]], the unifacial cambium of ''Lepidodendron'' lycopsid produced only secondary xylem. As the lycopods aged, the wood produced by the unifacial cambium decreased towards the top of the plant such that terminal twigs resembled young ''Lepidodendron'' stems. Compared to modern trees, the stems and branches of the lycopsids contained little wood with the majority of mature stems consisting of a massive [[Cortex (botany)|cortical]] [[meristem]]. The nearly-uniform growth of this cortical tissue indicates no difference in growth during changing seasons, and the absence of dormant [[bud]]s further indicates the lack of [[seasonality]] in ''Lepidodendron'' species.<ref name="Geography" /> The outermost cortex of oldest stems developed into the bark-like [[lycopodiopsid]] [[periderm]].<ref name="Evo">{{cite book |author=Karl J. Niklas |title=The Evolutionary Biology of Plants |publisher=University of Chicago Press |year=1997 |isbn=9780226580838 |edition=illustrated |page=321}}</ref> The bark of the lycopsid was somewhat similar to that of ''[[Picea]]'' species, as [[leaf scar]]s formed peg-like projections that stretched and tore as the bark stretched. To resist the bending force of wind, ''Lepidodendron'' depended on their outer bark rather than their vascular tissues, as compared to modern trees that rely mostly on their central mass of wood.<ref name="Students" />

=== Leaves ===
[[File:Lepidodendron leaf.jpg|thumb|left|Leaf of ''Lepidodendron''|200x200px]]
The leaves of the lycopsid were needle-like and were densely spiraled about young shoots, each possessing only a single [[Leaf vein|vein]]. The leaves were similar to those of a fir in some species and similar to those of ''[[Pinus roxburghii]]'' in others, though in general the leaves of ''Lepidodendron'' species are indistinguishable from those of ''[[Sigillaria]]'' species. The [[decurrent]] leaves formed a cylindrical shell around branches. The leaves were only present on thin and young branches, indicating that, though the lycopsid were evergreen, they did not retain their needles for as long as modern conifers. 
The leaf-cushions were fusiform and elongated, growing at most to a length of {{Cvt|8|cm|in|frac=2}} and a width of {{Cvt|2|cm|in|frac=4}}. The middle of leaf-cushions were smooth, where [[leaf scar]]s were created when an [[abscission]] layer cut a leaf from its base. Each leaf scar was composed of a central circular or triangular scar and two lateral scars that were smaller and oval-shaped. This central scar marks where the main [[vascular bundle]] of the leaf connected to the vascular system of the stem. This xylem bundle was composed only of primary [[Vessel element|trachea]].{{Citation needed|date=January 2024|reason=trachea instead of tracheids in lycophytes?}} The two outer scars mark the forked branches of a strand of vascular tissue that passed from the [[Cortex (botany)|cortex]] of the stem into the leaf. This forked strand is sometimes referred to as the "parichnos". Surrounding this strand were [[parenchyma]] cells and occasionally thick-walled elements. Surrounding both conducting tissues was a broad sheath of transfusion [[tracheid]]s. Below the leaf scar the leaf-cushion tapered to a basal position. In this tapering area, circular impressions with fine pits were present. These impressions were continuous with the parichnos scars near the top of the tapering portion. This is because the impressions are formed by [[aerenchyma]] tissue that developed in closely with the parichnos. Above the leaf scar was a deep triangular impression known as the "ligular pit" for its similarities to the [[ligule]] of ''[[Isoetes]]''. In some leaf-cushions a second depression was present above the ligular pit. Though its purpose is unclear, it has been suggested that the depression may mark the position of a [[sporangium]]. As the branch of a ''Lepidodendron'' lycopsid grew the leaf-cushion only grew to a certain extent, past which the leaf-cushion stretched. This stretching widened the groove that separated the leaf-cushions, creating a broad, flat channel.<ref name=Students/>

=== Underground Structures ===
The underground structures of ''Lepidodendron'' and similar lycopsid species known from the fossil record including ''[[Sigillaria]]'' are assigned to the form taxon, ''[[Stigmaria]]''. The rootlets were dichotomously branched from the [[rhizomes]] similar to ''Isoetes''. These rhizomorphic axes were shoot-like, and dichotomous branching of the rootlets structured the stigmarian systems. Rootlet scars can be seen from ''Stigmaria'' fossils where the root hairs used to be attached.<ref name="Hetherington">{{cite journal |last1=Hetherington |first1=A.J. |last2=Berry |first2=C.M. |last3=Dolan |first3=Liam |title=Networks of highly branched stigmarian rootlets developed on the first giant trees |journal=PNAS |date=2016 |volume=113 |issue=24| pages=6695–6700 |doi=10.1073/pnas.1514427113|doi-access=free |pmid=27226309 |pmc=4914198 |bibcode=2016PNAS..113.6695H }}</ref> [[Hypha]]e are occasionally present in the tissues of ''Lepidodendron'' lycopsids, indicating the presence of [[mycorrhiza]]l associations.<ref>{{cite journal |last1=Strullu-Derrien |first1=Christine |last2=Strullu |first2=Désiré-Georges |title=Mycorrhization of fossil and living plants |journal=Comptes Rendus Palevol |date=November 2007 |volume=6 |issue=6–7 |pages=483–494 |doi=10.1016/j.crpv.2007.09.006|bibcode=2007CRPal...6..483S }}</ref>

=== Decay ===
[[File:Estonian Museum of Natural History Specimen No 193541 photo (g23 g23-26 1 jpg).jpg|thumb|''Lepidodendron sp.'' bark from the [[Estonian Museum of Natural History]].|213x213px]]
Different [[fossil]] genera have been described to name the various levels of decay in ''Lepidodendron'' bark fossils. The name ''Bergeria'' describes stems that have lost their epidermises, ''Aspidiariu'' is used when cushions have been removed by deep decay, and ''Knorria'' is used when the leaf cushions and the majority of cortical tissues has decayed, with a shallow "fluted" surface remaining. However, it has been suggested that these are more likely growth forms than preserved bark types, as entire fossilized trunks have been discovered with dissimilar forms; if decay is assumed to be constant throughout the trunk, then different forms indicate growth rather than levels of decay. It is likely that the trunk of ''Lepidodendron'' lycopsids were subject to the growth forms ''Knorria'', ''Aspidiaria'', and ''Bergeria'' progressing up the trunk, respectively.<ref>{{cite journal |title= A rediscovered 114-foot Lepidodendron from Bolton, Lancashire |author= Thomas, B.A. and Watson, Joan |journal= Geological Journal |volume= 11 |number= 1 |pages= 15–20 |year= 1976 |publisher= Wiley Online Library |doi= 10.1002/gj.3350110102 |bibcode= 1976GeolJ..11...15T }}</ref>