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, which are common in both temperate and tropical 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 is actively 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). A current focus is on the Verbenaceae, a mostly New World family distributed primarily in Central and South America with its center of diversity in Argentina. This is an ongoing project with research at different levels of the phylogeny.
- Understanding the evolution of gene families is another interest in the Olmstead lab. Current projects include an analysis of the rubisco small subunit gene to better understand the mechanisms of concerted evolution, whereby multiple copies of a gene become homogenized over time, rather than diverging as mutations accumulate. Other studies are using nuclear gene families and studies of multiple genes to understand evolutionary processes at the level of species diversification.
- 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.
- An effort to establish a rigorous phylogenetic tree all angiosperms is underway in collaboration with several labs around the US. In this project, sequences of whole chloroplast genomes for representative species of important lineages will be combined with a selection of 15 or more genes sequences of many species of those lineages to resolve some of the remaining difficult nodes in the angiosperm tree. The Olmstead lab is contributing to the work in the Asteridae.