Editing Isoetes (section)

===Description===
Like the rest of the Lycopodiopsida class, ''Isoetes'' reproduces with spores.<ref name="Taylor-1992">{{Cite journal|last1=Taylor|first1=W. Carl|last2=Hickey|first2=R. James|date=1992|title=Habitat, Evolution, and Speciation in Isoetes|url=https://www.jstor.org/stable/2399755|journal=Annals of the Missouri Botanical Garden|volume=79|issue=3|pages=613|doi=10.2307/2399755|jstor=2399755}}</ref> Among the lycophytes, both ''Isoetes'' and the [[Selaginellaceae]] (spikemosses) are [[Heterospory|heterosporous]], while the remaining lycophyte family [[Lycopodiaceae]] (clubmosses) is [[homosporous]].<ref>{{Cite journal|date=2016|title=A community-derived classification for extant lycophytes and ferns|journal=Journal of Systematics and Evolution|language=en|volume=54|issue=6|pages=563–603|doi=10.1111/jse.12229|s2cid=39980610|issn=1759-6831|doi-access=free}}</ref> As heterosporous plants, fertile Isoetes sporophytes produce megaspores and microspores, which develop in the megasporangia and microsporangia.<ref name="Farmer-1890">{{Cite journal|last=FARMER|first=J. BRETLAND|date=1890|title=On Isoetes lacustris, L.|url=https://www.jstor.org/stable/43234433|journal=Annals of Botany|volume=5|issue=17|pages=37–62|jstor=43234433|issn=0305-7364}}</ref> These spores are highly ornate and are the primary way by which species are identified, although no one functional purpose of the intricate surface patterns is agreed upon.<ref>{{Cite journal|last=Hickey|first=R. James|date=January 1986|title=Isoetes Megaspore Surface Morphology: Nomenclature, Variation, and Systematic Importance|url=http://dx.doi.org/10.2307/1547394|journal=American Fern Journal|volume=76|issue=1|pages=1–16|doi=10.2307/1547394|jstor=1547394|issn=0002-8444}}</ref> The megasporangia occur within the outermost [[Microphylls and megaphylls|microphylls]] (single-veined leaves) of the plant while the microsporangia are found in the innermost microphylls.<ref name="La Motte-1933">{{Cite journal|last=La Motte|first=Charles|title=Morphology of the Megagametophyte and the Embryo Sporophyte Ofisoetes Lithophila|date=April 1933|url=http://doi.wiley.com/10.1002/j.1537-2197.1933.tb08887.x|journal=American Journal of Botany|language=en|volume=20|issue=4|pages=217–233|doi=10.1002/j.1537-2197.1933.tb08887.x}}</ref> This pattern of development is hypothesized to improve the dispersal of the heavier megaspore.<ref name="Taylor-1992" /> These spores then germinate and divide into mega- and micro- gametophytes.<ref name="Farmer-1890" /><ref>{{Cite journal|last1=SCOTT|first1=D. H.|last2=HILL|first2=T. G.|date=1900|title=The Structure of Isoetes Hystrix|url=https://www.jstor.org/stable/43235515|journal=Annals of Botany|volume=14|issue=55|pages=413–454|doi=10.1093/oxfordjournals.aob.a088787|jstor=43235515|issn=0305-7364}}</ref><ref name="La Motte-1937">{{Cite journal|last=LA MOTTE|first=CHARLES|date=1937|title=Morphology and Orientation of the Embryo of Isoetes|url=https://www.jstor.org/stable/42906582|journal=Annals of Botany|volume=1|issue=4|pages=695–715|doi=10.1093/oxfordjournals.aob.a083498|jstor=42906582|issn=0305-7364}}</ref> The microgametophytes have antheridia, which in turn produce sperm.<ref name="La Motte-1937" /> The megagametophytes have archegonia, which produce egg cells.<ref name="La Motte-1937" /> Fertilization takes place when the motile sperm from a microgametophyte locates the archegonia of a megagametophyte and swims inside to fertilize the egg.

Outside of heterospory, a distinguishing feature of ''Isoetes'' (and ''[[Selaginella]]'') from other [[pteridophyte]]s, is that their gametophytes grow inside the spores.<ref name="Farmer-1890" /><ref name="La Motte-1937" /><ref name="La Motte-1933" /> This means that the gametophytes never leave the protection of the spore that disperses them, cracking the [[perispore]] (the outer layer of the spore) just enough to allow the passage of gametes. This is fundamentally different from ferns, where the gametophyte is a photosynthetic plant exposed to the elements of its environment. However, containment creates a separate problem for Isoetes, which is that the gametophytes have no way to acquire energy on their own. ''Isoetes'' sporophytes solve this problem by provisioning starches and other nutrients to the spores as an energy reserve for the eventual gametophytes.<ref name="La Motte-1937" /><ref>{{Cite journal|last1=Abeli|first1=Thomas|last2=Mucciarelli|first2=Marco|date=2010|title=Notes on the Natural History and Reproductive Biology of Isoëtes malinverniana|url=https://www.jstor.org/stable/41237871|journal=American Fern Journal|volume=100|issue=4|pages=235–237|doi=10.1640/0002-8444-100.4.235|jstor=41237871|s2cid=83658338|issn=0002-8444}}</ref> Although not a homologous process, this provisioning is somewhat analogous to other modes of offspring resource investment in seed-plants, such as fruits and seeds. The extent to which resources provisioned to the megaspore also support the growth of the new sporophyte is unknown in ''Isoetes''.