Systematics and Paleobotany of the Legume Subfamily Caesalpinioideae

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9527673 Herendeen The large plant family Leguminosae (Fabaceae) is ecologically significant (nitrogen fixing species are common) and economically important (it includes soybeans, clovers, and tropical tree crops). While general aspects of taxonomic diversity are well known, many questions remain unanswered about evolutionary changes within the family that have led to the 18,000 or so species currently recognized. Even the closest relatives of the family remain controversial, with recent molecular (DNA) findings suggesting the small, herbaceous family Polygalaceae, with flowers superficially similar to "papilionoid" blossoms of Leguminosae. The most primitive groups of legumes are shrubs and trees classified in the subfamily Caesalpinioideae, with most genera placed in the tribes Amherstieae and Detarieae. Dr. Patrick Herendeen of Field Museum is working on these groups, emphasizing collection and analysis of fossil materials and integration of these data with information collected from living members of the subfamily studied by himself and by collaborators Anne Bruneau (DNA analyses), Ian Ferguson (pollen morphology), and Shirley Tucker (floral morphology). Extensive field work in Africa, a region of great species diversity for the two tribes, will provide new specimens and materials for all these researchers and others interested in legume systematics and evolution. Fossil studies will concentrate on flowers, pollen, fruits, and leaves collected from Eocene and Miocene deposits in Asia, Europe, and North America. Several extinct genera are known or suspected, with plants distinguished by combinations of features not found in modern, living species. Character analysis of this fossil material will help in determining the direction of evolutionary change in various floral and vegetative features, and in turn this will aid taxonomists in delimiting subtribal and generic groupings and in hypothesizing phylogenetic lineages within early legumes.