Isoetopsida
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The Isoetopsida is a class of the Lycopodiophyta. All living plants belong to the genus Isoetes in the order Isoetales. The order Isoetales is sometimes placed in the class Isoetopsida, sometimes in the Selaginellopsida or Lycopsida. There are 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 is the "scale trees" (order Lepidodendrales), which include Lepidodendron. These massive trees flourished in marshlands of the Carboniferous. Quillworts are considered by some to be the last remnant of such fossil trees, with which they share some unusual features including the development of both wood and bark, a modified shoot system acting as roots, bipolar growth, and an upright stance.
