Summary of leaves in the genera of Maloideae (Rosaceae)

The persistence, complexity, lobing, margins, venation, texture, shape, adaxial glands, and heteroblastic nature of leaves are summarized for all 28 genera of Maloideae. The leaves can be simple with entire, toothed, or pinnately lobed margins, or they can be pinnately compound. They can be deciduous to evergreen, thin and membranaceous to very coriaceous; they have either camptodromous or craspedodromous secondary venation and come in a wide variety of shapes. Leaves of mature foliage on short shoots can differ markedly from those on juvenile or long shoots. The amount of variation within a genus is often correlated with the number of species, with the large genera Malus, Pyrus, Aria, and Crataegus having the greatest diversity. Within a genus only a limited number of leaf types occur. The diversity of leaves in Maloideae may be due to a multifarious original gene pool that arose with the polychotomous, amphipolyploid origin of the subfamily resulting from hybridization between early members of the Spiraeoideae and Amygdaloideae.