Dissertation Research: Systematics and Biogeography of Mentzelia (Loasaceae): A North and South American Desert Disjunct

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Mentzelia, one of the few New World amphitropical plant disjuncts proposed to have originated in North America, will be examined for genetic divergence and phylogenetic relationships by graduate student Alice Hempel, under the supervision of adviser Robert Jansen at the University of Texas. Examination of such New World disjunctions using DNA restriction site information has not been done previously. The use of chloroplast DNA, nuclear ribosomal DNA and morphological data will generate three independent data sets to investigate the potential processes leading to the current distribution such as long distance dispersal, vicariance events, relict distributions and convergent evolution. Disjunct species and genera have been comparatively well documented between the arid lands of North America and South America, but no robust phylogenies exist for these taxa to interpret the biogeographical processes. This project is designed to answer systematics questions such as the relationships between the three Loasaceae subfamilies, the sections in Mentzelia and species within sect. Mentzelia, which contains the majority of South American species. A revision of sect. Mentzelia, including molecular, chromosomal and SEM seed coat data is needed to complete a modern revision of the genus. Morphological and molecular data will be analyzed both separately and integrated, using parsimony methods. The resulting phylogenetic trees and measures of genetic divergence will be used to evaluate the hypotheses regarding the present distribution of Mentzelia.