Systematics, Phylogeny, and Pollination System Evolution in Callitrichaceae

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9307038 Philbrick Underwater pollination (hydrophily) is one of the most enigmatic pollination systems in flowering plants. Hydrophily requires the abandonment or modification of a suite of characters intimately tied to the dry, aerial flowering condition, and represents a shift in floral biology with profound consequences for flower and pollen morphology. The mechanical and biochemical modifications entailed in achieving wettability (underwater release and capture of pollen) raise significant adaptive obstacles not encountered during evolutionary shifts from one aerial pollination system to another. The goals of Dr. Philbrick's project are to probe questions concerning the evolution of water pollination using the genus Callitriche as an experimental system. Callitriche is the most appropriate group to conduct these studies because it is the only genus of angiosperms that includes both aerial and underwater pollination systems. Phylogenetic analysis using morphological and new DNA characters will provide an understanding of the direction of change in floral and pollen features across the species in the genus, and thereby help determine models of change in adaptation to underwater pollination. %%% Underwater pollination is one of the more bizarre adaptations found in certain groups of flowering plants. Dr. Philbrick is studying this phenomenon in an explicit phylogenetic framework for the ca. 50 species of the genus Callitriche that includes both underwater and aerial pollination systems. The direction of change in floral and pollen features can be determined, and in turn this knowledge will allow analysis of cellular and biochemical mechanisms responsible for new floral structure.