Appalachian quillwort (Isoetes appalachiana, sp. nov.; Isoetaceae), a new pteridophyte from the eastern United States

Isoetes appalachiana, sp. nov., is an element of the I. engelmannii complex of North America. Its distinct cytology, spore morphology, and distribution are illustrated and described. Although widely distributed in the eastern United States, it appears to be most common in the Appalachian Mountains. Isoetes appalachiana is tetraploid; it is suspected to be an allopolyploid which evolved from the chromosome doubling of I. × altonharvillii, the sterile hybrid between I. engelmannii (s. str.) and I. valida.