Research in the Olmstead lab focuses on the phylogenetic reconstruction of flowering plants by molecular methods and the use of phylogenetic inference to understand plant evolution. The group of plants that comprise the primary research emphasis is the subclass Asteridae, especially Lamiales and Solanales, which are particualarly common in Neotropical ecosystems and contain many economically important plant families, such as the mint family, Lamiaceae, and tomato/potato family, Solanaceae. Several species-rich genera in Western North America have been subject to recent studies in the lab and the flora of this region is a rich source of research projects that can explore fundamental questions of evolution and natural history. In addition, the lab has been involved with research on the overall phylogeny of green plants, from their roots in the green algae to the tips of flowering plants.

Some current projects include the following:

- The Lamiales are a large clade of flowering plants in the Asteridae that include approximately 20 familes and 20,000 species. Much of the research in the lab in recent years has focused on the phylogeny and evolution of this large group. Several large complex groups (large genera or generic complexes) have been the subject of Ph.D. dissertations, including Mimulus (Phrymaceae), Castilleja (Orobanchaceae), Tabebuia (Bignoniaceae), and the Verbena complex (Verbenaceae). At a broader scale, an overall goal of the lab is to resolve systematic relationships among all of the major lineages in the Lamiales. Much of our recent focus has been on resolving the relationships of the polyphyletic Scrophulariaceae and determining where the various parts of that group belong (Olmstead et al., 2001; Oxelman et al., 2005; Tank et al., 2006). Our current focus is on the families Bignoniaceae and Verbenaceae. Both are primarily New World in distribution with centers of diversity in Central and South America and each includes ca. 700-800 species. We are using these large clades to study patterns of diversification throughout the Neotropics, including such questions as: When did dispersal from South to Central America occur? What was the origin of disjunct distributions between deserts of South and North America that are observed in several genera in these families? To what extent has the evolution into novel biomes led to increased diversification in these families?

- Solanaceae are one of the most important families of flowering plants, with numerous plants of agricultural, pharmaceutical, and horticultural importance. Several studies of specific groups have provided detailed knowledge of some branches within Solanaceae, and have contributed to an overall understanding of this family. Ongoing research in this group involves the use of transposable elements to mark polyploid events in phylogenetic history and a collaboration with Argentine botanists on the relationships of Petunia to its relatives in the genus Fabiana, a group of xeric-adapted shrubs.