Systematics/Phytogeography / Taxonomie/ Section
Kron, Kathleen A. , Bush, Catherine M. .
Evolutionary relationships among the lepidote rhododendrons (Rhododendron subgenus Rhododendron; Ericaceae) based on molecular data.
Lepidote rhododendrons (Rhododendron subgenus Rhododendron) can be found in widely varying habitats across the Northern Hemisphere. They are most diverse at high elevations in the tropics of the southwest Pacific and the Himalaya. This study uses six genes and/or regions from 54 species that represent 24 of the 28 subsections recognized by Cullen in the last treatment of lepidote Rhododendron. Sampling also includes representatives of the Pogonanthum and the tropical Vireya groups. Both parsimony and Bayesian analyses of chloroplast data alone result in poorly resolved trees with little statistical support at most nodes. The same general results are found when nuclear data are analyzed under both parsimony and Bayesian criteria. Estimated branch lengths in both chloroplast and nuclear data sets are short, especially at the deeper nodes. Due to no apparent conflict among data sets the chloroplast and nuclear data were combined and analyzed together. Parsimony and Bayesian analyses resulted a well-resolved tree, but support was still low for most of the deeper nodes. The combined analysis indicated two major groups of lepidote rhododendrons. Neither of these groups correspond to the groupings suggested by Cullen based on morphology. The Vireya group has the most support for its topology, but based on this study these tropical lepidotes are not monophyletic and include some Northern Hemisphere taxa. Two of the isolated lepidote species are found nested within the Himalayan taxa. Rhododendron minus is endemic to southeastern North America and is placed as sister to a clade containing R. racemosum, R. tomentosum, and R. formosum. Rhododendron ferrugineum is endemic to Europe and placed as sister to a group that includes both Himalayan taxa and boreal representatives such as R. tomentosum. The placement of these isolated taxa within the phylogeny of the lepidotes poses interesting biogeographical questions concerning the history of Rhododendron.
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1 - Wake Forest University, Department of Biology, PO Box 7325, Winston-Salem, North Carolina, 27109-7325, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Room 3/Woodward
Date: Monday, July 28th, 2008
Time: 5:15 PM