Dissertation Research: Phylogenetic Patterns and Molecular Divergence among Intercontinentally Disjunct Species of Styrax (Styracaceae)

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9310979 Philbrick and Fritsch Intercontinental plant disjunctions are ideal systems with which to examine models of geohistorical change. The flowering plant genus Styrax provides one such system, with several species of the Series Imbricatae occurring in California and in the Mediterranean region. This group plus 21 other living plant groups sharing a similar distributional pattern have been proposed as "Madrean-Tethyan" links based on morphological similarity: relicts of a once widespread dry habitat-adapted vegetation belt stretching from southwestern North America trans-Atlantically to central Asia in the early Tertiary. Alternative hypotheses for the existence of these intercontinental disjunctions claim no evidence for a Madrean-Tethyan corridor and maintain that taxa on either side of the Atlantic only appear closely related, but have actually been derived independently from mesic ancestors that migrated across either the Bering or the North Atlantic land bridges. The objective of the work by graduate student Fritsch under the direction of Dr. Philbrick is to test the Madrean-Tethyan continuity hypothesis using Styrax as a representative group by producing independent lines of evidence generated from morphological, DNA, and protein data. %%% Genetic distance measures generated from isozyme and chloroplast DNA variation within and among populations of Styrax will estimate taxon divergence times, whereas phylogenetic reconstruction of Series Imbricatae using morphological, chloroplast DNA, and nuclear ribosomal DNA characters will test the monophyletic status of the group. Analysis of the data will provide information indicating which model of Madrean-Tethyan history is likely to be correct as well as provide a sound classification of these plants for continuing taxonomic and evolutionary studies. ***