Dissertation Research: A Biosystematic Investigation of the Genus Cornus in the Americas

在教授顾问Robert Wilbur博士的指导下，杜克大学的研究生Zack Murrell将研究墨西哥山茱萸物种，最终目标是从世界范围的角度对山茱萸属进行分类修订。野外采集将有助于研究物种内和物种之间在植物结构特征(总体生长形式)、茎颜色、果实颜色和生境方面的差异。将收集种子，以便在共同的花园环境中种植植物，检查发芽要求，并研究幼苗的形态。收集的材料将用于扫描电子显微镜研究、染色体研究、解剖学研究和生长发育模式研究。山茱萸属(Cornus)由大约60种组成，生长在东亚、太平洋西北部、北美东部和墨西哥山区的温带地区。虽然所有的山茱萸都有相似的叶、花和短柔毛，但它们在生长形式(乔木、灌木和多年生草本植物具有木质根茎)和植物上的花排列上表现出很大的差异，从开放的分枝结构到被艳丽的白色叶子(苞片)包围的紧密排列的花头。区分物种的尝试一直存在争议，不得不依赖于深奥字符的细微差异。Murrell多方面研究的完成将极大地提高我们对山茱萸变异的理解，并为世界范围内的分类学修订奠定基础。

Under the guidance of faculty adviser Dr. Robert Wilbur, graduate student Zack Murrell of Duke University will study the Mexican species of dogwoods with the ultimate goal of providing a taxonomic revision of the genus Cornus from a worldwide perspective. Field collections will facilitate study of variation within and between species in features of plant architecture (overall growth form), stem color, fruit color, and habitat. Seeds will be collected in order to grow the plants in a common-garden environment, to examine germination requirements, and to study seedling morphology. The collected material will be used in scanning electron microscopy studies, chromosome investigations, anatomical studies, and examination of developmental patterns of growth. The dogwood genus, Cornus, comprises a group of approximately 60 species growing in temperate regions of eastern Asia, Pacific Northwest, eastern North America, and the mountains of Mexico. Although all the dogwoods have similar leaves, flowers, and pubescence, they exhibit great variation in growth forms (trees, shrubs, and perennial herbs with woody rhizomes) and in the arrangement of flowers on the plants, which can vary from an open branched structure to a tightly packed head of flowers surrounded by showy white leaves (bracts). Attempts to distinguish species have been controversial and have had to rely upon subtle differences in recondite characters. Completion of Murrell's multifaceted study will improve greatly our understanding of variation in the dogwoods and set the stage for a worldwide taxonomic revision.