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Abstract Detail

Systematics Section

Plunkett, Gregory M. [1], Lowry, Porter P. II [2], Nicolas, Antoine N. [3].

Incongruence among phylogenies of Melanesian Schefflera (Araliaceae): evidence from four plastid and three nuclear markers.

The large genus Schefflera (c. 900+ species) is polyphyletic, but “Melanesian Schefflera” represents a monophyletic group of ~50 species from the SW Pacific Islands. Within this clade, five subgroups have been recognized on the basis of morphology (known informally as the Canacoschefflera, Dictyophlebia, Dizygotheca, Gabriellae, and Plerandra groups). Earlier studies based on nuclear ITS and ETS sequence data suggested that Plerandra and Dictyophlebia were each monophyletic and most closely related, suggesting that stamen polymery is a synapomorphy for these clades. Further, the Gabriellae and Canacoschefflera groups were both monophyleltic, with the exception of Schefflera veillonorum, whose placement remained unresolved. By contrast, ITS and ETS data suggested that the Dizygotheca group forms two distinct clades, one of which represents the earliest divergence in Melanesian Schefflera. This polyphyly was especially surprising given the morphological distinctiveness of the tetraploid Dizygotheca group, including its inflorescence structure and its doubled anther sacs. To test these results, we assembled two additional data sets, based on (1) four plastid markers (psbA-trnH, ndhF-rpl32, rpl32-trnL, and trnE-trnT) and (2) a fragment of the nuclear RPB2 gene. Preliminary plastid results provide a different picture of relationships in Melanesian Schefflera: the Plerandra group is the earliest diverging lineage, and is not sister to Dictyophlebia; Canacoschefflera (including S. veillonorum) and Gabriellae form a single clade, but Gabriellae appears to be paraphyletic; and Dizygotheca is monophyletic. RPB2 data are too preliminary to infer detailed interspecific relationships, but do provide evidence of three distinct copies in Melanesian Schefflera. Results from the RPB2 gene suggest that the incongruence between ITS/ETS and the plastid sequence data may reflect differential lineage sorting of variable copies of rDNA after a genome duplication event.

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1 - New York Botanical Garden, Cullman Program for Molecular Systematics, 209 Southern Blvd., Bronx, NY, 10458, USA
2 - Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri, 63166
3 - Virginia Commonwealth University, Department of Biology, P.O. Box 842012, Richmond, Virginia, 23284

plastid sequences

Presentation Type: Oral Paper:Papers for BSA Sections
Session: 66
Location: Maybird/Cliff Lodge - Level C
Date: Wednesday, July 29th, 2009
Time: 2:15 PM
Number: 66006
Abstract ID:908