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See list of 8 species in this genus

The size and ornamentation of mature megaspores, found in the expanded leaf bases, are crucial for confident identification of most species. Collections of Isoetes from most of the growing season will possess only fragile, yellow-white, and largely unornamented megaspores. For most New England taxa, collections from August and later will yield identifiable material. It is recommended that collectors check the condition of the megaspores while in the field to insure that mature spores are available (they should be spherical in orthospecies and bone white upon drying). Hybrids are to be expected where 
two or more species are found in the same water body. Hybrid quillworts can be detected 
by their polymorphic megaspores that range in shape from spherical to pyramidal and flattened. References: Eaton (1900), Kott and Britton (1983), Taylor et al. (1993).

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 Show photos of:   Each photo represents one species in this genus.