Gostel, Morgan R. , Plunkett, Gregory , de Villiers, Bernard J. , Lowry, Porter P. II .
African-Malagasy Schefflera (Araliaceae), revisited: Expanded sampling reveals insights into morphological and biogeographic patterns.
The genus Schefflera, the largest within Araliaceae (~900+ species), has a pantropical distribution, however it is massively polyphyletic. Within Schefflera sensu lato, five clades have been identified, each with a distinct geographic affinity. One of these clades contains all species endemic to continental Africa and Madagascar, nearly 50 species in total. Previous studies have confirmed the monophyly of this clade and have also identified two subclades, loosely corresponding to the genera Neocussonia and Astropanax. Geographically, both subclades have representatives in Madagascar and in continental Africa. Molecular evidence from previous work has suggested origins for each of them in the continent, but these findings were based on limited sampling. In the present study, we have doubled the number of species sampled, from 19 to 40, and have expanded the set of molecular markers from two to five to include both nuclear (ITS & ETS) and plastid (ndhF-rpl32, trnK-rps16 & rpl32-trnL) sequence data. Our results demonstrate strong support for the monophyly of African-Malagasy Schefflera and its two subclades (Neocussonia and Astropanax). Evidence supporting continental origins is confirmed, with more complex biogeographic relationships emerging, including evidence of later radiations from Madagascar back to Africa. Classically employed morphological characters have been evaluated for congruence; certain widely used features such as inflorescence structure are poorly correlated with phylogenetic relationships. Convergence can be seen in other characters, particularly among Malagasy species from both clades, which display a tendency toward unifoliate leaves, a rare trait in Schefflera. Further indications reveal some surprises at the species level among the more morphologically diverse members of the Astropanax clade. Results demonstrate paraphyly with respect to the most widespread species, Schefflera myriantha, which is distributed throughout Africa, the Comoros islands, and Madagascar. S. myriantha from continental Africa appears sister to a clade containing both Malagasy representatives as well as S. monophylla. This finding suggests that Malagasy S. myriantha, while morphologically coherent, may represent a distinct lineage from its African ancestors.
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1 - Virginia Commonwealth University, Department of Biology, 1000 West Cary St., Room 126, Richmond, VA, 23284-2012, USA
2 - New York Botanical Garden, Cullman Program for Molecular Systematics Studies, 200th Street and Kazimiroff Boulevard, Bronx, New York, 10458, USA
3 - University of Johannesburg, Department of Botany and Plant Biotechnology, P.O. Box 524, Auckland Park, 2006, South Africa
4 - Missouri Botanical Garden, Africa & Madagascar Department, P.O. Box 299, St. Louis, MO, 63166-0299, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 556B/Convention Center
Date: Tuesday, August 3rd, 2010
Time: 1:30 PM