Isoetes, commonly known as the quillworts, is a genus of plants in the class Isoetopsida and order Isoetales. They are lycopods and the only genus in Isoetaceae. There are currently 192 recognized species, with a cosmopolitan distribution but often scarce to rare. Some botanists split the genus, separating two South American species into the genus Stylites, although molecular data place these species among other species of Isoetes, so Stylites does not warrant taxonomic recognition.