Morawetz, Jeffery J. , Steinmann, Victor W. , Riina, Ricarda , Jin, Wenchi , Mayfield, Mark H. , Yang, Ya , Berry, Paul E. .
The genus Euphorbia in the Flora of North America.
A group of seven contributors is preparing the treatment of the genus Euphorbia for Volume 12 of the Flora of North America. We are following the current broadly defined circumscription of the genus, including former segregate genera such as Chamaesyce, Pedilanthus, and Poinsettia. The latest molecular phylogeny of Euphorbia includes four roughly equal-sized clades, all of which are present in the Old World, where the genus presumably originated. In North America, there were probably multiple colonizations from Eurasia or Africa, but the large majority of the native North American species belong to Clade D (subgenus Chamaesyce). These include 24 species in section Agaloma, including showy species such as E. marginata and E. corollata. The largest block of species in Clade D is from sect. Chamaesyce, including 67 species centered in the southwestern U.S., but extending throughout the U.S. and southern Canada. Lastly, there are five taxa in Clade D in sect. Portulacastrum, all from southeastern U. S. These species are disjunct from the remainder of the section in South America, and we are currently investigating with molecular tools if they are really sister to each other. In the mainly Eurasian Clade B (subgenus Esula), there are 16 species native to North America, and molecular evidence points to at least two separate introductions of this group from the Old World. There are 14 additional species in this clade that have become naturalized in the U.S. from Eurasia, including the pernicious weed, E. esula. Lastly, in Clade C (subgenus Euphorbia), there is one species in section Pedilanthus, and seven in section Poinsettia. There are no native or naturalized members of Clade A (subgenus Rhizanthium) in North America. Together, these total 133 species of Euphorbia (117 native and 16 naturalized) in the area of continental North America north of Mexico.
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1 - University of Michigan, Herbarium & Dept. Ecology and Evolutionary Biology, 3600 Varisty Drive, Ann Arbor, MI, 48108, USA
2 - Instituto de Ecología, Centro Regional del Bajío, A.P. 386, 61600 Pátzcuaro, Michoacán, Mexico
3 - The Kansas State University Herbarium, 116 Ackert Hall, Manhattan, Kansas, 66506, USA
Presentation Type: Poster:Posters for BSA Sections
Location: Event Tent/Cliff Lodge
Date: Monday, July 27th, 2009
Time: 5:30 PM