The Isoetopsida's a class of the Lycopodiophyta. All living plants belong to the genus Isoetes in the order Isoetales. The order Isoetales's sometimes placed in the class Isoetopsida, sometimes in the Selaginellopsida or Lycopsida. There're about 140-150 species, with a cosmopolitan distribution but often scarce to rare. Some botanists split the genus, separating two South American species into the genus Stylites. The most famous group within the Isoetopsida's the "scale trees" (order Lepidoden… (More on Isoetopsida)