Systematics Section / ASPT
Cacho, N. Ivalu , Baum, David A. , Berry, Paul E. .
Molecular systematics of the slipper spurges (Pedilanthus-Euphorbia clade-Euphorbiaceae).
The slipper spurges comprise the Pedilanthus clade (Euphorbia, Euphorbiaceae), a group of 15 species mostly occurring in seasonally dry forests in Mexico, Central America and the Caribbean. This is one of several small but distinctive groups that were previously recognized as separate genera based primarily on cyathium morphology but have since been found to be nested within the giant and morphologically diverse genus Euphorbia. Most of the 15 species in the Pedilanthus clade have a restricted distribution, nine being narrow endemics in Mexico. Species in the Pedilanthus clade manifest a remarkable diversity in life form, ranging from true evergreen treelets of tropical moist forests to succulent desert shrubs. The unifying synapomorphy for the clade is its bilaterally symmetric cyathium bearing a spur in which the nectar-glands are concealed. The spur varies greatly in shape and is thought to have coevolved in association with bird and insect pollinators.
The only published phylogenetic hypothesis for the Pedilanthus clade was based on a morphological assessment based on habit and floral morphology (Dressler 1957). Dressler suggested five groups of species. However, the relationships among the five proposed species groups remained ambiguous. More recently, two additional species were described, and additional populations of some rare species were located. A molecular phylogeny of the Pedilanthus clade is reconstructed here based on nuclear and chloroplast sequences. Results suggest two main clades. One includes mostly leafless succulent species, whereas the other consists of leafy shrubs or treelets. Implications regarding the evolution of succulence, and transitions from bird to hymenopteran pollination (and associated changes in cyathium morphology) are discussed.
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1 - University of Wisconsin-Madison, Department of Botany, Birge Hall, 430 Lincoln Drive, Madison, WI, 53706, USA
2 - University of Wisconsin Madison, Department of Botany, Birge Hall, 430 Lincoln Drive, Madison, Wisconsin, 53706-1381, USA
3 - University of Michigan, Department of Ecology & Evolutionary Biology, 830 North University Avenue, Ann Arbor, Michigan, 48109-1048, USA
tropical dry forest
Presentation Type: Oral Paper:Papers for Sections
Location: Stevens 3/Hilton
Date: Wednesday, July 11th, 2007
Time: 11:00 AM