Indeterminate leaves of Chisocheton (Meliaceae): survey of structure and development

Abstract

Pinnately compound leaves in the Malesian genus Chisocheton (Meliaceae) have leaf-tip buds that continue to produce new pinnae (leaflets) periodically for many years. Juvenile leaves form a terminal pinna in place of the leaf-tip bud found in adult leaves. The histology of an old leaf-tip bud is similar to the entire leaf primordium in other species of Meliaceae with large pinnate leaves (e.g. Chukrasia and Dysoxylum) which serve as examples of more typical leaves. Pinna initiation from this meristem continues after the first stage of leaf expansion as seen in the relatively constant number of pinna primordia in a large sampling of leaf-tip buds of varying ages. Structure and development are compared in leaves of nine species of Chisocheton, out of a total of approxiamtely 50 species in the genus. Species having small leaves (e.g. C. pentandrus) show more branch-like, indeterminate leaf growth as compared with species with large leaves (e.g. C. macranthus). The structure and development of leaves of Chisocheton are like the similar indeterminate leaves of the American and African genus Guarea. Some authors have used the indeterminate leaves of Chisocheton and Guarea as examples of intermediate organs showing ‘fuzzy morphology’ or ‘partial homology.’ Nevertheless, these unusual organs are considered here as being homologous with leaves of other Meliaceae based on their position, histology and ontogeny. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 139, 207–221.