My research all revolves in one way or another around understanding phylogeny. My empirical work focuses primarily on plant diversity and evolution. In particular, I have long term interests in Viburnum and Dipsacales, and in the origin and early evolution of flowering plants. In collaboration with former students, postdocs, and lab visitors, I have also published molecular phylogenetic analyses of a number of other angiosperm groups. And, with former postdoc David Hibbett I have published a series of papers on the phylogeny of basidiomycetes, especially shiitake mushrooms.
I have also worked on a number of conceptual or theoretical issues. Specifically, I have been interested in the notion of species, in patterns in the distribution of homoplasy, in character evolution and comparative methods, in phylogenetic nomenclature, and in combining data from various sources. But I've published on some other conceptual issues, including methods for assessing the direction of evolution, the analysis of large data sets, and identifying shifts in diversification rate. Finally, I helped build and still coordinate the development of a relational database of phylogenetic knowledge called TreeBASE.
Previous graduate students and postdocs in the lab have worked on a wide variety of projects, but again these are united by an interest in phylogeny. In general, graduate student dissertation projects have entailed working with some group of organisms (usually a plant group), but have tended to also involve some theoretical work. For example, Mike Sanderson worked on a large legume clade, Astragalus, and linked this to theoretical work on homoplasy. Likewise, George Weiblen combined empirical work on the phylogeny of figs and fig wasp with theoretical work on comparing phylogenies and on using phylogenies to understand the structure of ecological communities. To the extent that it seems reasonable, I've also tried to encourage a side project or two. For example, Rick Ree has been pursuing an interest in methods for inferring rates of character change in a phylogeny.
Several of my interests are not yet well reflected in publications. In particular, I have been doing field work in China over the last four years, especially in the eastern Himalayan region of Qinghai, Sichuan, and Yunnan. Some of the information on these trips is now in a specimen database on the web. This work connects with another major interest: the biogeography and the historical assembly of plant communities around the Northern Hemisphere.