Steinmann, Victor W. , Berry, Paul E. .
Subgeneric classification of the North American Euphorbia (Euphorbiaceae).
With over 2000 species, Euphorbia (Euphorbiaceae) ranks among the five largest genera of Angiosperms. Approximately 350 species occur in continental North America. Its immense size and ample distribution have hindered taxonomy of the genus, and a modern, comprehensive infrageneric classification is lacking. During the second half of the 20th century the most widely employed subgeneric classification recognized five subgenera in the New World (subg. Agaloma, subg. Chamaesyce, subg. Esula, subg. Euphorbia, and subg. Poinsettia) and an additional two closely related segregate genera (Cubanthus and Pedilanthus). However, there has been no general consensus, and the subgenera Chamaesyce and Poinsettia were often treated as independent genera. Recent molecular phylogenetic studies have greatly improved our understanding of relationships within the genus. These studies demonstrate that Euphorbia is composed of four early diverging lineages, each strongly supported to be monophyletic and containing hundreds of species. Furthermore, results indicate that all segregate genera are nested within the genus and that the subgenera Agaloma, Esula, and Euphorbia are either poly- or paraphyletic. Based on this research, a refined subgeneric classification of the North American species is proposed. Three subgenera are recognized (subg. Chamaesyce, Esula, and Euphorbia), but their circumscription is drastically different from how they have been historically defined. Within these subgenera, 16 morphologically characterized sections are proposed. The traditionally recognized subg. Esula is divided into five sections: sect. Esula, sect. Tithymalus, sect. Portulacastrum and two undescribed sections. Of these five, only the first two are retained in subg. Esula, and the remainder belong to subg. Euphorbia. The composition of the traditionally recognized subg. Poinsettia is unchanged, but it is treated as sect. Poinsettia. The composition of the traditionally recognized subg. Chamaesyce is also unaltered, but the correct name at the rank of section is sect. Anisophyllum. The segregate genera Pedilanthus and Cubanthus are treated as sect. Crepidaria and sect. Cubanthus, respectively. Subgenus Agaloma, as formerly considered, is divided into sect. Alectoroctonum and three undescribed sections.
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1 - Instituto de Ecología, A.C., Centro Regional del Bajío, Avenida Lázaro Cárdenas 253, Col. Centro, Pátzcuaro, Michoacán, 61600, Mexico
2 - University of Michigan, Herbarium & Dept. Ecology and Evolutionary Biology, 3600 Varisty Drive, Ann Arbor, MI, 48108, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Ballroom B/Convention Center
Date: Monday, August 2nd, 2010
Time: 3:00 PM