Angiosperm leaves are both well-identifiable and morphologically diverse organs. They are well characterized by their developmental origin as inherently bifacial outgrowths of the shoot apical meristem. As bifacial organs, they develop a margin at the border of their adaxial and abaxial faces. This leaf margin is a crucial developmental-morphological element accounting for much of the leaf diversity generated during evolution. Two aspects of margin-related morphological diversification of leaves are discussed: (1) ontogenetic fusion and secondary loss of margins underlying gamophyllous, peltate, and unifacial morphologies; (2) marginal organ formation leading to dissected leaves with more or less well separated sub-blades. Current evidence for genetic control of these developmental processes in different angiosperm clades are discussed.

Key words: bifaciality, blastozone, margin fusion, organ formation competence, Ranunculidae