Britannica
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Where do quillworts grow, and how many Isoetes species are known?
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Lycophyte
Club moss (Lycopodium annotinum).
Quillworts, which belong to the order Isoetales, are aquatic or semi-aquatic lycophytes that primarily inhabit swampy, cooler regions of North America and Eurasia. While most species grow submerged in fresh water for all or part of the year, terrestrial species are typically found in seasonally wet habitats where they die back to their corm when the soil dries.12
Regarding their diversity, the Pteridophyte Phylogeny Group (PPG I) recognizes approximately 250 species within the genus Isoetes.12