We are working on the evolution, biogeography, and systematics of flowering plants. A particular interest is the evolution of sexual systems, including dioecy, androdioecy, heterodichogamy, and sex change. We are also studying chromosome rearrangements in Cucumis and Araceae, and plant sex chromosomes, focusing on the Cucurbitaceae Bryonia and Coccinia. Biogeographic work has focused on tropical as well as temperate families and continues to lead to the discovery of new species as well as floristic and monographic treatments. In much of this work, molecular clocks and their calibration with fossils play a large role. Last not least, we are interested in the evolution and mode of inheritance of plant introns.