Global plant diversity patterns: case studies from early branching legume clades

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All recent studies suggest that species diversity is distributed very evenly through time, across geographical regions and amongst lineages in phylogenetic history. Although it is widely believed that increased variability drives species diversification, teasing apart the causes of diversification remains a challenge. Research in my laboratory focuses on systematics, phylogenetics and evolution of the economically important plant family Leguminosae (Fabaceae). With 765 genera and c. 19,500 species, legumes are the third largest flowering plant family, represent one of the most spectacular examples of evolutionary diversification in plants, and occur in nearly every biome across the globe. We study the mostly tropical basal lineages of the family. The long term objective of my research is to use comprehensively sampled, robust and well-resolved phylogenies to establish stable classifications and to better understand macro-evolutionary morphological, ecological and biogeographical patterns. Three objectives will be addressed in the next five years. 1) We will examine global patterns of diversification to test for significant rate shifts across and within the five basal legume clades. To achieve this, we will generate comprehensively sampled phylogenies using a phylogenomics approach to sequence 100's of nuclear genes. Rate shifts will be studied in relation to geography, biomes, functional traits and floral evolution. 2) Intrinsic plant-related characteristics will be studied to test for trait-dependent diversification. Floral characters will be examined in Detarioideae and Dialioideae, two lineages that exhibit remarkable diversity in floral morphology, and functional traits related to habitat adaptations will be studied in Caesalpinioideae, where radiations into all major biomes have occurred. 3) Biogeography and biome evolution will be studied in Detarioideae and Dialioideae to determine whether the distribution of these primarily wet forest clades can be traced to an early to mid-Eocene, dry environment diversification, as suggested for most legumes. Using fossil calibrated phylogenies, we will investigate present-day geographic and ecological distributions, infer ancestral biomes, look for evidence of biome shifts and critically evaluate the relative importance of biome conservatism versus geological history in explaining the distribution of these two clades. Our recent work has made significant progress towards a more robust and stable phylogenetically-based classification of legumes. The research proposed here offers scope to consolidate these efforts to clearly understand patterns of legume diversity across the globe. This collaborative and broadly based research program provides opportunities for training of students in plant systematics and evolution, which are essential to a better understanding of existing biodiversity worldwide.