A large group of vascular plants characterised by having parenchymatous leaf gaps in the stele (vascular system of the stem) and by having leaves which are thought to have originated in the distant past as branched stem systems. Some botanists regard the Pteropsida as a natural group which they recognise as a class, subdivision, or division. Others regard it as an artificial assemblage of plants that have undergone certain similar changes from a rhyniophyte ancestry. The various components of the Pteropsida are here treated as three separate divisions under the names Magnoliophyta, Pinophyta, and Polypodiophyta.