The true thistles (genus Cirsium) are highly diverse, taxonomically problematic, and ecologically and economically important components of north temperate floras worldwide. Minimal genetic variation across species has hampered resolution of relationships in Cirsium but can now be overcome with the identification of three highly variable, nuclear gene regions that provide phylogenetic information at fine-scale levels within the genus. Phylogeny of the true thistles will be studied by comparing DNA sequences from three nuclear gene regions (G3pdh, the B1 promoter, and histidine kinase). Hypotheses to be tested include: (1) Do the ecologically diverse New World thistles constitute a natural group? (2) Are the New World species (especially the Californian endemics) good examples of adaptive radiation? (3) Did the New World thistles arise from a common European or Asian ancestor? (4) Is Cirsium distinct from the closely related genus Carduus? Resolution of natural groupings within Cirsium also will be used to replace the prevailing, highly unnatural, sectional classification of the genus. Achieving a natural classification of Cirsium is critically important to provide a biologically meaningful framework for future basic and applied research on true thistles. This research will have the broader impacts of enriching undergraduate education at the University of California, Berkeley. Undergraduate students will be enlisted in the efforts and will participate in laboratory research. The project will also involve at-risk, ethnically diverse high school students, who will be introduced to biological research and will participate in growing research plants. By defining natural species groups within Cirsium, this research will aid biological-control researchers in choosing new agents for controlling non-native weedy thistles. Land resource professionals and the lay public will be instructed in the conservation of rare thistles by means of a field workshop, and a larger group will have access to results on the Jepson Online Interchange website, thereby obtaining information on the importance of modern systematic approaches to understanding regional plant diversity and classification.
