Dissertation Research: Systematics and Flower Development in the Milkweed Tribe Gonolobeae (Asclepiadaceae)

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Schaal, Raven, and Prinzie Graduate student Thomas Prinzie, under the direction of Dr. Barbara Schaal at Washington University and Dr. Peter Raven at the Missouri Botanical Garden, is studying the evolutionary relationships and flower morphology of a neotropical group of milkweed vines (tribe Gonolobeae in the family Asclepiadaceae). Milkweed flowers are highly specialized as a result of complex fusion between floral parts and the presence of unique corona structures. During field work in Texas and Southern Mexico, Mr. Prinzie has collected fresh flowers of some 60 species, allowing him to study their structure in great detail using both standard anatomical sectioning techniques and scanning electron microscopy. By collecting information at many stages of development, it will also be possible to trace the origin of the various corona structures, whose diversity has confused taxonomists in the past. A second component of the research consists in reconstructing the evolutionary history of this tribe of milkweeds, on the basis of DNA sequence data from two separate nuclear and chloroplast genes. The resulting phylogenetic information will complement other studies being performed at higher taxonomic levels in this and closely related families. By studying the structure and development of Gonolobeae flowers in the framework of an independently established phylogeny, it will be possible to clarify the evolutionary modifications that gave rise to their great diversity, and to illustrate the role of developmental changes as a mechanism of diversification.