Editing Lycopodiopsida (section)

==Characteristics==
Club-mosses (Lycopodiales) are homosporous, but the genera ''[[Selaginella]]'' (spikemosses) and ''[[Isoetes]]'' (quillworts) are heterosporous, with female spores larger than the male.<ref>{{cite book | url=https://books.google.com/books?id=0rWZDwAAQBAJ&dq=Gametophyte+%28G%29+and+sporophyte+%28S%29+sexual+systems&pg=PA62 | title=Transitions Between Sexual Systems: Understanding the Mechanisms of, and Pathways Between, Dioecy, Hermaphroditism and Other Sexual Systems | isbn=978-3-319-94139-4 | last1=Leonard | first1=Janet L. | date=21 May 2019 | publisher=Springer }}</ref> As a result of fertilisation, the female gametophyte produces sporophytes. A few species of ''Selaginella'' such as ''[[Selaginella apoda|S.&nbsp;apoda]]'' and ''[[Selaginella rupestris|S.&nbsp;rupestris]]'' are also [[Viviparity|viviparous]]; the gametophyte develops on the mother plant, and only when the sporophyte's primary shoot and root is developed enough for independence is the new plant dropped to the ground.<ref name=Awas09/> Many club-moss [[gametophyte]]s are [[Myco-heterotrophy|mycoheterotrophic]] and long-lived, residing underground for several years before emerging from the ground and progressing to the [[sporophyte]] stage.<ref name=WintFrie08/>

Lycopodiaceae and spikemosses (''Selaginella'') are the only vascular plants with biflagellate sperm, an ancestral trait in land plants otherwise only seen in [[bryophyte]]s. The only exceptions are ''Isoetes'' and ''Phylloglossum'', which independently has evolved multiflagellated sperm cells with approximately 20 flagella<ref>{{cite journal | url=https://www.tandfonline.com/doi/abs/10.1080/20013591099209 | doi=10.1080/20013591099209 | title=Motile Gametes of Land Plants: Diversity, Development, and Evolution | date=2001 | last1=Renzaglia | first1=Karen S. | last2=Garbary | first2=David J. | journal=Critical Reviews in Plant Sciences | volume=20 | issue=2 | pages=107–213 | bibcode=2001CRvPS..20..107R | url-access=subscription }}</ref><ref>[http://www.bio-nica.info/biblioteca/Judd2002Cap7.pdf An Overview of Green Plant Phylogeny]</ref> (sperm flagella in other vascular plants can count at least thousand at most, but the number is generally much lower, and flagella are completely absent in seed plants except for Ginkgo and cycads).<ref>{{cite journal | pmc=5406480 | date=2017 | last1=Alvarez | first1=L. | title=The tailored sperm cell | journal=Journal of Plant Research | volume=130 | issue=3 | pages=455–464 | doi=10.1007/s10265-017-0936-2 | pmid=28357612 | bibcode=2017JPlR..130..455A }}</ref> Because only two flagella puts a size limit on the genome, we find the largest known genomes in the clade in ''Isoetes'', as multiflagellated sperm is not exposed for the same selection pressure as biflagellate sperm in regard of size.<ref>{{cite book | url=https://books.google.com/books?id=6BFV8wb7SWkC&dq=Lycopodiaceae+Phylloglossum+biflagellate+sperm&pg=PA312 | title=Plant Genome Diversity Volume 2: Physical Structure, Behaviour and Evolution of Plant Genomes | isbn=978-3-7091-1160-4 | last1=Greilhuber | first1=Johann | last2=Dolezel | first2=Jaroslav | last3=Wendel | first3=Jonathan | date=13 November 2012 | publisher=Springer }}</ref>