Evolution and function of leaf venation architecture: A review

The leaves of extant terrestrial plants show highly diverse and elaborate p atterns of leaf venation. One fundamental feature of many leaf venation pat terns, especially in the case of angiosperm leaves, is the presence of anas tomoses. Anastomosing Veins distinguish a network topologically from a simp le dendritic (tree-like) pattern which represents the primitive venation ar chitecture. The high degree of interspecific variation of entire venation p atterns as well as phenotypic plasticity of some venation properties, such as venation density, indicate the high selective pressure acting on this br anching system. Few investigations deal with functional properties of the l eaf venation system. The interrelationships between topological or geometri c properties of the various leaf venation patterns and functional aspects a re far from being well understood. In this review we summarize current know ledge of interrelationships between the form and function of leaf venation and the evolution of leaf venation patterns. Since the functional aspects o f architectural features of different leaf venation patterns are considered , the review also refers to the topic of individual and intraspecific varia tion. One basic function of leaf venation is represented by its contributio n to the mechanical behaviour of a leaf. Venation geometry and density infl uences mechanical stability and may affect, for example, susceptibility to herbivory. Transport of water and carbohydrates is the other basic function of this system and the transport properties are also influenced by the ven ation architecture. These various functional aspects can be interpreted in an ecophysiological context. (C) 2001 Annals of Botany Company.