Professor at Yale University (2000-2022), Harvard University (1992-2000), the University of Arizona (1985-1992), and San Diego State University (1982-1985). Director of the Harvard University Herbaria (1995-1999), the Yale Peabody Museum of Natural History (2003-2008), the Marsh Botanical Garden (2015-2018), and the Yale Institute of for Biospheric Studies (2019-2021). His research concerns the diversity and evolutionary history of plants, and connections between phylogeny, biogeography, and ecology. Many of his empirical studies have focused on Viburnum and other Dipsacales.
