Taxonomy, identity, and status of Isoetes virginica (Isoetaceae)

The quillwort Isoetes virginica was described from material from a single location in west central Virginia in 1937. Subsequent treatments have considered it to be either a rare Virginia endemic, a synonym of Isoetes melanopoda or as a broadly defined taxon including the Piedmont endemic Isoetes piedmontana. The discovery of a new population near the type locality and rediscovery of an historical station has permitted cytological and ecological investigations of the original species concept. These investigations establish that Isoetes virginica is tetraploid and provide additional morphological and ecological evidence for this distinct species. Characteristics separating Isoetes virginica from the morphologically similar Isoetes piedmontana and Isoetes melanopoda are discussed. A lectotype for Isoetes virginica is designated. This pteridophyte is considered a Virginia endemic with a total known population of about 350 plants.