SIMPLE AND COMPOUND LEAVES - REDUCTION OR MULTIPLICATION

Flowering plants can have either simple or compound leaves. Compound l eaves have an interesting evolutionary history, and arose independentl y in the ferns, cycads and flowering plants. The compound structure ma y be a consequence of simple leaves that are subdivided into separate leaflets; inherently different from simple leaves, and intermediate be tween shoots and leaves; or the leaf ground state, with suppression an d reduction leading to simple leaves. The knox genes have been extensi vely studied to determine their role in leaf initiation and developmen t, Preliminary evidence indicates that the simple and compound leaf ty pes, though superficially similar at the time of initiation, have diff erences that arise in the preprimordium stage in the shoot apical meri stem, Compound leaves in peas and tomato probably have independent ori gins from an ancestrally simple state in the basal angiosperms, Geneti c and molecular analyses of leaf morphogenesis in diverse organisms wi ll help determine whether independent origins of compound leaves gave rise to similar structures.