Leaf venation patterns and principles of evolution

Abstract

Leaf venation patterns (of dicots and for comparison of ferns) are analyzed according to form and function. From topological investigations of the gross vein system and the patterns of small veins forming areolae (vertices and adjacents, geometry of gross veins, scaling exponents) and from results of physiological anatomy and ecophysiology we deduce a major contribution of selforganization processes in the development of the angiosperm leaf vein system. The resulting plasiticity of the construction of small veins, allowing function under a variety of circumstances, is a prerequisite for the adaptation of angiosperms to very different environmental conditions. In the ontogenetic selforganization process of the small veins the phloem initiation probably acts as a pace-maker. Methods of morphodynamics and functional morphology are used to discuss, when, why and how this key invention for the angiosperm leaf arose during the evolutionary process.