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Isoetes
''Isoetes'', commonly known as the quillworts, is a genus of plants in the class Isoetopsida and order Isoetales. They are lycopods. There are about 140–150 species, with a cosmopolitan distribution but often scarce to rare. Some botanists split the genus, separating two South American species into the genus ''Stylites'', although molecular data place these species among other species of ''Isoetes'', so the genus does not warrant taxonomic recognition.
The name of the genus is sometimes spelled ''Isoëtes''. The diaeresis (two dots over the e) indicate that the o and the e are to be pronounced in two distinct syllables. Including this in print is optional; either spelling is correct.〔(International Code of Nomenclature for algae, fungi, and plants (Melbourne Code) ) see section 60.6〕
==Description==
Quillworts are mostly aquatic or semi-aquatic in clear ponds and slow-moving streams, though several (e.g. ''I. butleri'', ''I. histrix'' and ''I. nuttallii'') grow on wet ground that dries out in the summer. Quillwort leaves are hollow and quill-like, arising from a central corm. Each leaf is narrow, long (exceptionally up to ) and wide; they can be either evergreen, winter deciduous, or dry-season deciduous. They broaden to a swollen base up to wide where they attach in clusters to a bulb-like, underground rhizome characteristic of most quillwort species, though a few (e.g. ''I. 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 heterosporous. Quillwort species are very difficult to distinguish by general appearance. The best way to identify them is by examining the megaspores under a microscope.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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