Editing Selaginella (section)

== Description ==
''Selaginella'' species are creeping or ascendant plants with simple, scale-like leaves ([[microphylls]]) on branching stems from which roots also arise. The stems are aerial, horizontally creeping on the substratum (as in ''[[Selaginella kraussiana]]''), sub-erect (''[[Selaginella trachyphylla]]'') or erect (as in ''[[Selaginella erythropus]]''). The vascular [[stele (biology)|steles]] are polystelic [[protostele]]s. Stem section shows the presence of more than two protosteles. Each stele is made up of [[Xylem#Patterns of protoxylem and metaxylem|diarch]] (having two strands of xylem<ref>{{cite web |title=Diarch |url=https://www.thefreedictionary.com/diarch |website=The Free Dictionary}}</ref>) and [[Xylem#Patterns of protoxylem and metaxylem|exarch]] (growing outward in) [[xylem]]s.{{citation needed|date=January 2017}} The steles are connected with the cortex by means of many tube-like structures called [[trabeculae]], which are modified endodermal cells with [[casparian strips]] on their lateral walls.{{citation needed|date=January 2017}} The stems contain no pith.{{citation needed|date=January 2017}}

In ''Selaginella'', each microphyll and sporophyll has a small scale-like outgrowth called a [[ligule]] at the base of the upper surface.<ref name=Stace>{{cite book|last=Stace|first=C. A.|author-link = Stace, C. A.|year=2010|title=New Flora of the British Isles|edition=Third|publisher=Cambridge University Press|location = Cambridge, U.K.| isbn=9780521707725}}</ref>{{rp|7}} The plants are [[Heterospory|heterosporous]] with spores of two different size classes, known as megaspores and microspores.<ref>{{Cite journal|last1=Petersen|first1=Kurt B.|last2=Burd|first2=Martin|date=2018|title=The adaptive value of heterospory: Evidence from Selaginella|journal=Evolution|language=en|volume=72|issue=5|pages=1080–1091|doi=10.1111/evo.13484|pmid=29645092|s2cid=4800398|issn=1558-5646|doi-access=free}}</ref> In [[Selaginella rupestris]] fertilization takes place while the megaspore is still attached to the parent plant, and is only released after the embryo has produced [[cotyledon]]s and a root.<ref>[https://books.google.no/books?id=98DnyHnucoUC&pg=PA3&dq=S.+apus+S.+rupestris+embryo+sporophyte&hl=no&newbks=1&newbks_redir=0&sa=X&ved=2ahUKEwi87JOVm9SMAxUXIBAIHQfQNCIQ6AF6BAgHEAM#v=onepage&q=S.%20apus%20S.%20rupestris%20embryo%20sporophyte&f=false Tree Breeding for Genetic Improvement of Tropical Tree Species]</ref>

Unusual for the lycopods, which nearly always have [[Microphylls and megaphylls|microphylls]] with a single unbranched vein, the microphylls of a few ''Selaginella'' species contain a branched vascular trace.<ref>{{Cite journal |last1=Wagner |first1=Warren H. |last2=Beitel |first2=Joseph M. |last3=Wagner |first3=Florence S. |date=1982-11-19 |title=Complex Venation Patterns in the Leaves of Selaginella : Megaphyll-Like Leaves in Lycophytes |url=https://www.science.org/doi/10.1126/science.218.4574.793 |journal=Science |language=en |volume=218 |issue=4574 |pages=793–794 |bibcode=1982Sci...218..793W |doi=10.1126/science.218.4574.793 |issn=0036-8075 |pmid=17771037 |s2cid=44904740}}</ref>

Under dry conditions, some species of ''Selaginella'' can survive dehydration. In this state, they may roll up into brown balls and be uprooted, but can rehydrate under moist conditions, become green again and resume growth. This phenomenon is known as [[poikilohydry]], and poikilohydric plants such as ''Selaginella bryopteris'' are sometimes referred to as [[resurrection plants]].<ref name="Bailey1916">{{cite book|title=The Standard Cyclopedia of Horticulture|author=Liberty Hyde Bailey|publisher=The Macmillan company |year=1916 |volume=5 |pages=2920–2921; 3639 |url=https://books.google.com/books?id=EpMDAAAAMAAJ&pg=PA2920}}</ref>

There is no evidence of [[Paleopolyploidy|whole genome duplication]] in Selaginella's evolutionary history. Instead they have gone through tandem gene duplications, which is particularly noticeable in genes relevant for desiccation tolerance.<ref name="VanBuren">{{cite journal |last1=VanBuren |first1=Robert |last2=Ching |first2=Man Wai |last3=Ou |first3=Shujun |last4=Pardo |first4=Jeremy |last5=Bryant |first5=Doug |last6=Jiang |first6=Ning |last7=Mockler |first7=Todd C. |last8=Edger |first8=Patrick |last9=Michael |first9=Todd P. |title=Extreme haplotype variation in the desiccation- tolerant clubmoss ''Selaginella lepidophylla'' |journal=Nature Communications |date=2018 |volume=9 |issue=13 |page=13 |doi=10.1038/s41467-017-02546-5|pmid=29296019 |pmc=5750206 |bibcode=2018NatCo...9...13V }}</ref>{{Technical inline|date=May 2024}}

Their chloroplasts are missing about two-thirds of their plastidial [[Transfer RNA|tRNA]] genes, which are instead found in the genome of the [[cell nucleus|nucleus]].<ref>[https://www.pnas.org/doi/10.1073/pnas.2412221121 Extensive import of nucleus-encoded tRNAs into chloroplasts of the photosynthetic lycophyte, Selaginella kraussiana]</ref> The genus is unique among vascular plants in having species with monoplastidic cells, single giant chloroplasts, located mostly in their dorsal epidermal cells, but also in the upper mesophyll of some species. This appears to be a derived traits and an adaptation to low-light conditions, having originated at least twice. Cells with multiplastidic chloroplasts, more than ten chloroplasts per cell, are considered most basal, and are found in species exposed to more light. Oligoplastidic cells, cells with 3 to ten chloroplats, are more adated to weaker light, and the monoplastidic species being the most shade-loving forms. It is estimated that 70% of Selaginella species are monoplastidic. These receive just 0.4~2.1% of full sunlight, while species with multiple chloroplasts live in open places where they on average receive more than 40.5% of full sunlight.<ref>[https://bsapubs.onlinelibrary.wiley.com/doi/10.1002/ajb2.1455 Gigantic chloroplasts, including bizonoplasts, are common in shade-adapted species of the ancient vascular plant family Selaginellaceae]</ref>