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

亚洲东部和北美东部许多密切相关的植物物种的不连续分布是北方半球最迷人的地理格局之一。 这一惊人的现象几个世纪以来一直吸引着植物学家的注意，为系统的和植物地理学的研究提供了一个焦点。 尽管迄今为止的证据表明了一个复杂的历史，但两大洲之间的植物区系交流和拟议的迁移路线的相对重要性在很大程度上仍然不清楚。为了更好地了解生物地理格局，有必要对具有良好化石记录的植物群进行进一步研究。 山茱萸属，其中包括广泛种植的“花山茱萸”，是研究的理想模式。 有一个很好的化石记录和三个亚组显示洲际不连续的分布，属允许详细的定量，基于遗传学的间断分布模式的地理学研究。 北卡罗来纳州州立大学的Jenny Xiang博士提出的这项研究的主要目标是：1）利用来自多个基因的形态特征和DNA序列数据为山茱萸属建立一个强大的系谱学基础; 2）测试基于该属形态多样性评估的进化和地理学假设;（3）利用谱系框架评价该属主要物种形成事件的时间（地质意义上）。 将在美洲和中国进行广泛的实地考察，以收集一些物种目前无法获得的植物材料。将通过一个在线网页向公众提供历史资料，该网页将作为今后开发一个可通过网络查阅、这一高度栽培和地理学上重要的植物属的分类学专著。该研究的重点是山茱萸属，以促进我们目前对东亚历史性质的理解-北美东部植物区系交流，通过整合系统发育和地理数据，和DNA为基础的定年方法，使用化石记录提供的校准点。 尽管在欧洲和北美的分类群是众所周知的，但热带和亚洲的山茱萸却鲜为人知，研究不足。研究中产生的多个分子数据集也将有助于比较不同基因的进化模式和克里思，以加强对这两个孤立大陆分子进化的理解。 在线网页将最大限度地利用从研究中获得的系统发育和植物地理信息，这将是有价值的评估保护优先事项（帮助指导研究山茱萸炭疽病，并制定战略，可持续利用山茱萸的自然资源），和未来的生态，药理学和园艺研究。 一名研究生将通过这项研究进行培训。 学生参与的机会是重要的，因为它对系统学，生物多样性科学的未来有着深远的影响。

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.