Complex Venation Patterns in the Leaves of <i>Selaginella</i> : Megaphyll-Like Leaves in Lycophytes

Abstract

Venation patterns of the leaves of two lycophytes, Selagiella adunca and Selaginella schaffneri, do not fit the definition of microphylls as having a single, unbranched vein. Although S. adunca has a simple pattern, S. schaffneri has a complexity matching that of many megaphylls, with numerous branching veins. The veins of S. schaffneri undergo an average of 13 branchings (range, 8 to 21), and reticulation between veins is frequent. The discovery of this radical departure from the familiar microphylls of lycophytes indicates that complex venation patterns in leaves do not necessarily arise from fusion of whole branches. The microphyll may not be as structurally stable as formerly believed.