Heteroblastic sequence and leaf development in Leea guineensis

The leaves initiated at successive nodes in the heteroblastic series in Leea guineensis seedlings become progressively more complex in construction. Leaves at the first four nodes are simple and are followed by transitional forms between nodes 5 and 7. These transitional leaf forms are compound in nature, and intermediates such as deeply lobed leaves are not observed. At successively higher nodes, the compound nature of the leaves becomes progressively more complex. The most common sequence of leaf morphologies is simple (nodes 1-4), trifoliate to pinnate (nodes 5-7), bipinnate (by node 8), and tripinnate (by node 11). The developmental morphology of the simple leaves in the sequence was markedly different from the compound leaves that followed. However, the early stages of development of the compound leaves, regardless of their degree of complexity, were very similar. Therefore, there appears to be a striking developmental distinction between the simple leaves and the compound leaves in the sequence. Simple leaf primordia become centrally concave and assume a characteristic folded appearance, whereas compound leaves have up to three orders of branching and are structurally more complex. However, compound leaves of different levels of complexity seem to share certain developmental features. At its maximum, the compound nature of the leaf can best be described in terms of subunits of seven leaflets. Thus, the complexity of the leaf can be viewed as a reiteration of the basic unit. The increase in compound leaf complexity does not alter the rate of leaf production.