Phylogenetic Study of the Dogwood Genus Cornus L. (Cornaceae)

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Xiang0129069The discontinuous distribution of many closely related plant species in eastern Asia and eastern North America is one of the most fascinating biogeographic patterns in the Northern Hemisphere. This striking phenomenon has attracted the attention of botanists for centuries, providing a focal point for systematic and biogeographic investigation. Although evidence available so far has suggested a complex history, the floristic exchange between the two continents and relative importance of proposed migration routes have largely remained unclear. Additional studies of plant groups with a good fossil record is necessary for a better understanding of the biogeographic pattern. The dogwood genus Cornus L., which contains several ornamentally and medicinally important plants including the widely planted "flowering dogwood", is an ideal model for the study. With an excellent fossil record and three subgroups showing intercontinentally discontinuous distributions, the genus permits a detailed quantitative, phylogeny-based biogeographic study of disjunct distribution patterns. The primary goals of the proposed study by Dr. Jenny Xiang at North Carolina State University are: 1) to build a robust genealogical foundation for the dogwood genus using morphological characters and DNA sequence data from multiple genes; 2) to test evolutionary and biogeographic hypotheses that were based upon assessments of the morphological diversity in the genus; and 3) to evaluate the timing (in a geological sense) of major speciation events in the genus using the genealogical framework. Extensive fieldwork will be conducted in the Americas and China to collect plant materials that are currently not available for some species. Historical information will be made available to the public via an on-line web page, which will serve as a starting point for the future development of a web-accessible, taxonomic monograph of this highly cultivated and biogeographically important plant genus.The study focuses on the genus Cornus to advance our current understanding of the historical nature of eastern Asian-eastern North American floristic exchange through integration of phylogenetic and biogeographic data, and DNA-based dating approaches using calibration points provided by the fossil record. Despite well known taxa in Europe and North America, tropical and Asiatic dogwoods are poorly known, and understudied. The multiple molecular data sets generated in the study will also facilitate comparisons of mode and tempo of evolution of different genes to enhance the understanding of molecular evolution in the two isolated continents. The on-line web page will maximize the utility of the phylogenetic and biogeographic information obtained from the study, which will be valuable for evaluating conservation priorities (help in guiding research on the dogwood anthracnose disease, and developing strategies for sustainable uses of natural sources of dogwoods), and future ecological, pharmacological, and horticultural research. One graduate student will be trained through this study. The opportunity for student participation is important for it has profound impact on the future of systematics, the science of biodiversity.