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

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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.