The Isoetopsida is a class of the Lycopodiophyta. All living species belong to the genus Selaginella in the Selaginellales or to Isoetes in the order Isoetales. In the past, members of this group have sometimes been placed in the class Isoetopsida, sometimes in the Selaginellopsida or Lycopodiopsida. There are about 700 species of Selaginella and 140-150 species of Isoetes, with a cosmopolitan distribution but often scarce to rare. Some botanists split Isoetes, separating two South American species into the genus Stylites.