Systematics/Phytogeography / Taxonomie/ Section
Neubig, K. M. , Whitten, W. M. , Williams, N. H. , Silvera, Katia , Cushman, John C. , Dalstrom, Stig .
Systematics of Oncidiinae (Orchidaceae) and the Evolution of Crassulacean Acid Metabolism.
The subtribe Oncidiinae, including the well known genus Oncidium, contains approximately 1500 species in almost 90 genera. Although molecular systematic studies have been made on portions of this subtribe, the relationship between several genera remains unresolved. This study has examined approximately 600 species (represented by over 700 OTUs) in 77 genera. Our results confirm the placement of the traditionally recognized Ornithocephalinae and Telipogoninae subtribes within the Oncidiinae. Although many genera in Oncidiinae are shown to be monophyletic, the most notable exception is the genus Oncidium, which is a highly polyphyletic assemblage of species that has been traditionally recognized based on floral morphology. This convergent floral morphology has been shown to be part of an oil rewarding Malpighiaceae mimicry system. Plants in Oncidiinae are common features of neotropical habitats and have adapted to many different niches (e.g., on cacti and on the twigs of trees). Because the plants have taken advantage of different ecological niches, different metabolic systems have evolved throughout the subtribe. Carbon isotopic composition of leaf material of Oncidiinae species shows a bimodal distribution with most species exhibiting peak values near -27‰, suggesting a C3 photosynthetic pathway, or around -15‰, suggesting a CAM pathway. High quality leaf RNA samples were obtained from closely related orchid species from the subtribe Oncidiinae with a range of photosynthetic pathways from C3 photosynthesis to weak or strong CAM showing that at least five isoforms are present in orchids, with one putative CAM-specific PEPC isogene identified in CAM and weak CAM species. This interdisciplinary project integrates ecophysiological, biochemical and molecular genetic approaches to understand the evolutionary origins of CAM within the context of a highly resolved phylogeny of Oncidiinae.
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1 - University of Florida, Department of Botany, 220 Bartram Hall, P.O. Box 118526, Gainesville, Florida, 32611-8526, USA
2 - University of Florida, Department of Botany, Florida Museum of Natural History, P.O. Box 117800, Gainesville, Florida, 32611-7800, USA
3 - University of Florida, Florida Museum of Natural History, Gainesville, Florida, 32611-7800, USA
4 - University of Nevada, Reno, Department of Biochemistry & Molecular Biology, MS 200, Reno, Nevada, 89557-0014, USA
5 - Marie Selby Botanical Gardens, Orchid Identification Center, 811 South Palm Avenue, Sarasota, Florida, 34236, USA
Crassulacean acid metabolism (CAM)
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, July 29th, 2008
Time: 3:00 PM