Bolander's Quillwort: Isoetes bolanderi (Synonyms: Isoetes bolanderi var. bolanderi, 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)
Midget Quillwort: Isoetes minima (Synonym: Isoetes howellii var. minima)
Nuttall's Quillwort: Isoetes nuttallii (Synonyms: Isoetes nuttallii var. nuttallii, Isoetes opaca, Isoetes suksdorfii)
Western Quillwort: Isoetes occidentalis (Synonyms: Isoetes flettii, Isoetes lacustris, Isoetes lacustris var. paupercula, Isoetes paupercula, Isoetes piperi)
Bristle-like Quillwort, Spiny-spored Quillwort: Isoetes tenella (Synonyms: Isoetes braunii, Isoetes echinospora, Isoetes echinospora var. braunii, Isoetes echinospora var. muricata, Isoetes muricata, Isoetes setacea)