Milkweeds are well known flowering plants of temperate North America. They have been widely studied by pollination biologists, evolutionary biologists, and chemical ecologists, and have served as a model system in studies of plant-insect coevolution. They are perhaps best known as the host plant of the Monarch butterfly - the discovery of the role of cardiac glycosides produced by milkweeds and sequestered by Monarchs for use against avian predators was a classic development in evolutionary ecology. However, research on milkweed species relationships has lagged far behind the tremendous progress in studies of the population biology and chemistry of milkweeds. A much deeper understanding of well-studied ecological and evolutionary processes and the ability to assess the generality of these phenomena will be gained from this investigation of the phylogenetic relationships among milkweed species. Research by Dr. Mark Fishbein at Mississippi State University will result in an improved classification of the milkweed genus (Asclepias), analyses of past and current hybridization, and elucidation of the biogeographic link between North American and African species. The inferred phylogeny of Asclepias will be used as a framework for answering several key evolutionary and biogeographic questions: 1) Are all American milkweeds derived from a single African colonist, or are several ancestrally African lineages represented among the American species?, 2) Did milkweeds arrive in North America via a North Atlantic crossing or via South America?, and 3) Is there evidence for past hybridization and introgression between morphologically disparate species that are no longer capable of hybridization? Elucidating the evolutionary history of Asclepias will give important insights into a group that has given rise to ubiquitous weeds and some of the rarest species in North America. It also will provide a crucial basis for future studies of the coevolution of milkweeds and their specialist insect herbivores. The results of this project will likely impact disciplines beyond systematics, evolution, and ecology. Milkweeds are increasingly being used in horticulture as garden perennials and cut flowers. Increased understanding of milkweed relationships will foster development of new horticultural materials by identifying close relatives of cultivated species that can be grown using established protocols. Studies of plant chemistry based on milkweeds will be enhanced, especially research targeting pesticide development. Because of the importance of Asclepias species as the primary host plant of the Monarch butterfly, this project will contribute to the conservation of threatened Monarch butterfly populations. Field and laboratory work with Mexican colleague Zamudio Ruiz and British colleague D. J. Goyder will enhance international collaboration. In addition, the PI is developing milkweed as a model system for understanding how hybridization occurs between species, which is critical for understanding the ecological impacts of genetically modified organisms. This project will significantly impact graduate and undergraduate training in molecular systematics and evolutionary biology. Mississippi State University provides an excellent opportunity to increase the research opportunities of underrepresented groups in biological sciences. Students will present the results of their research at regional and national meetings.