Systematics Section / ASPT
Chuba, David , Fishbein, Mark , Goyder, David J. , Chase, Mark W. .
Phylogeny and Biogeography of the African Asclepias complex (Apocynaceae).
The phylogeny and biogeography of the African Asclepias generic complex (Apocynaceae) were determined. The Asclepias complex is a group that, due to the difficulty in utilizing only morphological characters for generic classification, has historically been subject to various taxonomic treatments. This study employed phylogenetic analysis based on the chloroplast rpl16 intron, trnC-rpoB spacer and trnS-G spacer/trnG intron. Parsimony and Bayesian analyses were used to evaluate recently proposed generic circumscriptions and to investigate African biogeography. Biogeographic analyses were conducted using DIVA to determine directionality and sequence of biogeographic events. Pergularia and Kanahia + Calotropis, genera of Asclepiadinae that are excluded from the broadest circumscription of Asclepias, were found to be successive sisters to a clade that includes all species associated with Asclepias s.l. There was weak support for sister clades composed entirely of either African or American species. Within the African subclade, a number of currently recognized genera are either para- or polyphyletic. For example, a clade that includes Aspidoglossum breve, A. ovalifolium, A. delagoense, and Schizoglossum hamatum was well supported, whereas Aspidoglossum heterophyllum was well supported as sister to Aspidonepsis flava. The study suggests that the union of Africa-Arabia with Iran during the middle Miocene may have triggered the initial entry of arid adapted plants, including ancestors of the African Asclepias complex, into North Africa via the arid Arabian subcontinent. This is suggested by the placement of Pergularia, Calotropis, and Kanahia, whose species mostly inhabit arid and semi-arid regions of the continent, as early diverging lineages of Asclepiadinae.
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1 - Portland State University, Biology Department, Po Box 751, Portland, Oregon, 97207-0751, USA
2 - Royal Botanic Garden, Kew, Herbarium, Richmond, Surrey, TW9 3AB, United Kingdom
3 - Royal Botanic Gardens, Kew, Jodrell Laboratory, Molecular Systematics Section, Richmond, Surrey, TW9 3DS, United Kingdom
Presentation Type: Oral Paper:Papers for Sections
Location: Stevens 2/Hilton
Date: Tuesday, July 10th, 2007
Time: 3:00 PM