Developmental and Structural Section
Ogburn, Matthew .
Anatomical variation in Cactaceae sensu lato.
Interpretation of the evolution of Cactaceae, a physiologically, ecologically, and morphologically distinctive angiosperm group, depends on a solid understanding of phylogenetic relationships both within and outside of the clade. Molecular approaches have begun to resolve these relationships and reveal 1) that Pereskia, the leafy genus long interpreted as the sister group of all other cacti, is likely paraphyletic, and 2) that Cactaceae is nested within a paraphyletic Portulacaceae as a member of the ‘ACPT clade’ (Anacampseroteae, Cactaceae, Portulaca, and Talinum). This information provides a framework for asking questions about important steps in the evolution and radiation of cacti. I examined vegetative anatomy in the ACPT clade with the goals of identifying potential synapomorphies at varying hierarchical levels, comparing conflicting phylogenetic hypotheses, and examining hypotheses about cactus evolution. Results indicate that Talinum retains many plesiomorphic characters supporting its position as sister to the rest of ACPT. Relationships between Cactaceae, Portulaca, and Anacampseroteae are as yet unclear, but the balance of morphological evidence appears to favor a sister-group relationship between Portulaca and Anacampseroteae. Potential synapomorphies for a clade of Cactaceae and Anacampseroteae include thick-walled sclereids in stem cortex, cortical initiation of periderm, and uni- or biseriate nodal hairs (areolar hairs in Cactaceae). Characters supporting a clade of Portulaca and Anacampseroteae include subterete, succulent leaves, loss of phloem fiber caps, and transversely oriented leaf stomata; other authors have also identified a base chromosome number of x=9. Finally, these results indicate that the gain of stem stomata and delayed bark, although precursors for the shift to stem photosynthesis, are not likely in themselves to have been key innovations that facilitated the radiation of cacti.
Log in to add this item to your schedule
1 - University of Missouri-St. Louis, Department of Biology, 1 University Boulevard, St. Louis, MO, 63121, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Boulevard C/Hilton
Date: Tuesday, July 10th, 2007
Time: 5:00 PM