Phylogenetic and Biogeographic Studies of the Dogwood Genus
Cornus L. (Cornaceae)
Abstract
The 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 the first detailed
quantitative, phylogeny-based biogeographic study of the genus. The primary
goals of the proposed study 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
related morphological diversity in the genus, and the timing of major speciation
events in the genus using the genealogical famework. 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. It will clarify relationships in this taxonomically highly controversial
genus, and add to accumulating evidence on a major, repeated, biogeographic
pattern. 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 (e.g., 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. The research will result in publication of articles in peer-reviewed
scientific journals in addition to the worldwide web tree of life. 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.