Bolander's Quillwort: Isoetes bolanderi (Synonyms: Isoetes bolanderi var. parryi, Isoetes bolanderi var. pygmaea, Isoetes californica, Isoetes pygmaea)
Howell's Quillwort: Isoetes howellii (Synonyms: Isoetes melanopoda, Isoetes melanopoda var. californica, Isoetes nuda, Isoetes underwoodii)
Nuttall's Quillwort: Isoetes nuttallii (Synonyms: Isoetes opaca, Isoetes suksdorfii)
Western Quillwort: Isoetes occidentalis (Synonyms: Isoetes flettii, Isoetes lacustris, Isoetes lacustris var. paupercula)