Taxonomy and Distribution of Isoetes valida

Isoetes valida constitutes an earlier valid name for I. caroliniana. This emergent aquatic, diploid quillwort is known from nine states along the Appalachian Mountains and Piedmont, growing in cold streams, mountain woodland ponds and in the saturated organic ooze of springs from central Pennsylvania to northeastern Alabama. It exhibits a distribution similar to several other endemic Appalachian pteridophytes. Disjunct populations are also known from the Coastal Plain of southeastern Alabama and Delaware. Although similar in appearance to I. engelmannii, I. valida is typically distinguished by its raggedly reticulate megaspore ornamentation, its velum covering 50% or more of the unmarked sporangium wall, and spinulose microspores.