The possession of two or more leaf types, often differing widely in morphology and function. For example, certain species of Lycopodium and Selaginella have two rows of expanded lateral leaves and one or two rows of smaller adaxial or abaxial leaves. Many aquatic and semiaquatic plants have dissected submerged leaves and entire floating or aerial leaves (see illustration). The submerged leaves are adapted to reduce resistance to water flow while the floating leaves have a broad lamina to maintain buoyancy. Compare heteroblastic development.  |
