Floral evolution and biogeography in early diverging legume lineages

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The proposed research program focuses on the evolution and systematics of early diverging lineages of tropical tree species belonging to the family Leguminosae (pea and bean family), subfamily Caesalpinioideae. The objectives are to reconstruct the evolutionary history of this subfamily and to test hypotheses concerning the evolution of floral and vegetative morphology, rates of diversification and biogeography. With nearly 20,000 species, the Leguminosae is the third largest and economically one of the most important of angiosperm families. Traditionally the Leguminosae is considered to comprise three subfamilies, the Caesalpinioideae, Mimosoideae and Papilionoideae. Of the three subfamilies, the Caesalpinioideae has been the most poorly studied taxonomically and phylogenetically. These early offshoots of the Leguminosae are highly diverse in their floral and vegetative morphology and widely distributed in the world with a fossil record that dates to the Eocene. They also encompass some of the first diverging lineages that include species which fix nitrogen. Using molecular data derived from the chloroplast and nuclear genomes, and building upon our previous work in the subfamily, we will identify natural groups and determine relationships among genera. This will serve as a framework for establishing a new, badly needed, classification system for the Caesalpinioideae. This new classification will allow us to explore patterns of floral and vegetative evolution, biogeographic patterns, and molecular evolution. Fossils will be used to document minimum ages of lineages, as historical points for testing biogeographical hypotheses, and as a basis for estimating taxonomic and molecular diversification rates. The proposed research is central to an international collaboration aimed at examining relationships in this poorly known, yet ecologically and taxonomically important, early diverging lineages of the Leguminosae. Our role is to provide a strongly supported phylogeny for comparative purposes with the aim of studying the evolution of pollen morphology, wood anatomy, floral ontogeny and nodulation in this diverse group of taxa.