Systematics Section / ASPT
Fishbein, Mark , Lynch, Steven P. , Chuba, David , Ellison, Chris , Goyder, David J. , Chase, Mark W. , Mason-Gamer, Roberta .
Phylogeny, Biogeography, and Systematics of Asclepias (Apocynaceae).
MILKWEEDS (Asclepias sensu lato, Apocynaceae) are familiar plants to North American and African naturalists, ecologists, and evolutionary biologists. Some species are well known in horticulture the world over and a few are considered agricultural pests. They are perhaps best known in North America as host plants of the Monarch butterfly and for the role they play in the chemical ecology of this species. They have served as a model system for studies of the evolutionary ecology of plant reproduction and increasingly in the study of plant defenses. However, phylogenetic study of this large (c. 400 spp.), well-known genus has lagged. We used DNA sequences of one nuclear (LEAFY intron) and three plastid (rpl16 intron, trnC-rpoB spacer, trnS-G spacer/trnG intron) loci to estimate the phylogeny of Asclepias in the broad sense. Phylogenetic estimates were obtained using standard parsimony and Bayesian approaches and alternative hypotheses were tested using likelihood-ratio tests. The biogeographic history of the group was explored using Dispersal-Vicariance Analysis and Bayesian approaches. We found that African and American milkweeds were reciprocally monophyletic, supporting recent efforts to remove all African milkweeds from Asclepias. All South American species fall into a single clade nested within the North American species. Currently recognized infraspecific taxa in Asclepias sensu stricto (i.e., in America) are largely polyphyletic and a dramatic reorganization of the classification is warranted. Most of the diversity of Asclepias in Mexico is centered in a single, large clade of species that characteristically inhabit montane habitats. The relationships among major clades are not well supported, presumably due to rapid diversification early in the history of milkweeds in the Americas.
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Evolution of defense traits of milkweeds
1 - Portland State University, Biology Department, Po Box 751, Portland, Oregon, 97207-0751, USA
2 - Louisiana State University-Shreveport, Biological Sciences, One University Place, Shreveport, Louisiana, 71115, USA
3 - Royal Botanic Gardens, Kew, Jodrell Laboratory, Richmond, Surrey, TW9 3AB, United Kingdom
4 - University of Illinois Chicago, Department of Biological Sciences, M/C 066, 845 W Taylor Street, Chicago, Illinois, 60607, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Wednesday, August 2nd, 2006
Time: 11:30 AM