My research deals primarily with the origin and early evolution of angiosperms. My oldest interest is in Cretaceous fossil pollen and leaves and their implications for the evolution, geographic spread, and original ecology of angiosperms. More recently my research has emphasized phylogenetic analyses of relationships between angiosperms and other seed plants and among living primitive angiosperm groups, based on morphological, molecular, and fossil evidence. I have worked on phylogeny, evolution, and biogeography of several living plant groups, especially the tropical family Annonaceae, the largest family of primitive angiosperms. My current main project aims to integrate Early Cretaceous fossils into the predominantly molecular phylogeny of living primitive angiosperms and to evaluate implications of the results for morphological evolution.