Isoetopsida

Taxobox
name = Isoetopsida

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image_width = 240px
regnum = Plantae
divisio = Lycopodiophyta
classis = Isoetopsida
subdivision_ranks = Orders
subdivision =
*Isoetales
*Lepidodendrales †
*Pleuromeiales †

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.