Editing Isoetes (section)

==Description==
[[File:Isoetes megasporangia L.jpg|thumb|right|upright|Quillwort megasporangia]]
Quillworts are mostly aquatic or semi-aquatic in clear ponds and slow-moving streams, though several (e.g. ''[[Isoetes butleri|I.&nbsp;butleri]]'', ''[[Isoetes histrix|I.&nbsp;histrix]]'' and ''[[Isoetes nuttallii|I.&nbsp;nuttallii]]'') grow on wet ground that dries out in the summer. The quillworts are spore-producing plants and highly reliant on water dispersion. Quillworts have different ways to spread their spores based on the environment. Quillwort [[leaf|leaves]] are hollow and quill-like, with a minute [[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=3rd |publisher=Cambridge University Press |location=Cambridge, U.K. |isbn=9780521707725}}</ref>{{rp|7}} arising from a central [[corm]]. The sporangia are sunk deeply in the leaf bases. Each leaf will either have many small spores or fewer large spores. Both types of leaf are found on each plant.<ref>{{Cite book |last=Levyns |first=M.R. |title=A Guide to the Flora of the Cape Peninsula |publisher=Juta & Company, Limited |year=1966 |edition=2nd Revised |oclc=621340}}</ref> Each leaf is narrow, {{convert|2|-|20|cm|sigfig=1}} long (exceptionally up to {{convert|100|cm|sigfig=1|disp=or|abbr=on}}) and {{convert|0.5|-|3.0|mm|2|abbr=on}} wide; they can be either [[evergreen]], winter [[deciduous]], or dry-season deciduous. Only 4% of total biomass, the tips of the leaves, is chlorophyllous.<ref name = "book - form&function">[https://books.google.com/books?id=YJFB4l262WkC&dq=Only+the+tips+of+the+leaves+are+chlorophyllous+%284%25+of+total+biomass%29&pg=PA171 Tropical Alpine Environments: Plant Form and Function]</ref>

The roots broaden to a swollen base up to {{convert|5|mm|1|abbr=on}} wide where they attach in clusters to a bulb-like, underground [[rhizome]] characteristic of most quillwort species, though a few (e.g. ''[[Isoetes tegetiformans|I.&nbsp;tegetiformans]]'') form spreading mats. This swollen base also contains male and female sporangia, protected by a thin, transparent covering (''velum''), which is used diagnostically to help identify quillwort species. They are [[spore|heterosporous]]. Quillwort species are very difficult to distinguish by general appearance. The best way to identify them is by examining their megaspores under a microscope. Moreover, habitat, texture, spore size, and velum provide features that distinguish Isoëtes taxa.<ref>Isoëtes Linnaeus, Sp. Pl. 2: 1100. 1753; Gen. Pl. ed. 5, 486, 1754.</ref> They also possess a vestigial form of secondary growth in the basal portions of its cormlike stem, an indication that they evolved from larger ancestors.<ref>[https://books.google.com/books?id=aKzSBAAAQBAJ&dq=%22The+extant+genus+Isoetes+possesses+a+vestigial+form+of+secondary+growth%22&pg=PA7 The Formation of Wood in Forest Trees: The Second Symposium Held under the Auspices of the Maria Moors Cabot Foundation for Botanical Research]</ref>