1Ecology. A plant that is adapted for a dry savannah environment; the growth form characteristic of such a plant.

2Botany and Palaeontology. Any of various extinct primitive vascular plants of the Upper Silurian and Devonian periods, lacking true roots and leaves but having a creeping rhizome and a cylindrical branching stem with a central vascular strand, sometimes bearing scales or leaf-like branchlets. Also: a member of the extant order Psilotales, comprising two genera (Psilotum and Tmesipteris) of small tropical and subtropical plants that superficially resemble these fossils.