Peirson, Jess , Berry, Paul , Riina, Ricarda .
Unraveling the origins and diversification of the New World leafy spurges.
The leafy spurges, Euphorbia subg. Esula, represent the main temperate radiation within the large genus Euphorbia. Species in subg. Esula are typically annual and perennial herbs with mostly alternate-leaved stems that terminate in an umbel-like arrangement of cyathia. The cyathia generally have 4 or 5 glands, sometimes with horn-like outgrowths. The subgenus contains about 500 species that are distributed primarily in temperate Eurasia, but with smaller, disjunct centers of diversity in the mountains of the Old World tropics, temperate areas of southern Africa, and the New World. We analyzed sequences of the nrITS and chloroplast ndhF regions to construct a worldwide phylogeny of the subgenus and to examine the origins and diversification of the 36 species native to the New World. Our taxon sampling represented over 60% of the species diversity within subg. Esula and produced a robust phylogenetic hypothesis for the clade. Our data indicate that the New World species resulted from multiple colonizations of subg. Esula from the Old World, and we infer four distinct origins. One species, E. trichotoma, is the sole New World member of sect. Paralias, which includes a number of littoral species from Europe and some of the Atlantic islands. Five other species belong to the large sect. Helioscopia, representing two separate introductions: one for the Appalachian, forest-dwelling, perennial E. purpurea and the other for four mainly annual species, including the widespread E. spathulata and the narrow Texas endemic, E. texana. Based on morphological evidence, this group also includes E. philippiana from southern Chile, the only member of subg. Esula native to South America. The majority of New World diversity (30 species), however, occurs in sect. Peplus, together with several species of Mediterranean origin. Our phylogenetic results suggest that the New World species of sect. Peplus fall into three primary clades: a southern United States clade of small, annual species and two clades of larger perennial species, one restricted to Mexico and Central America and the other from the western United States and northern Mexico. Like several other clades of Euphorbia, New World leafy spurges have diversified most in arid and montane regions of the southwestern United States and northern Mexico.
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1 - The University Of Michigan Herbarium, Department Of Ecology & Evolutionary Biology, 3600 Varsity Drive, Ann Arbor, MI, 48108-2228, USA
2 - University Of Michigan, Department Of Ecology And Evolutionary Biology, 830 N UNIVERSITY ROOM 2035, Ann Arbor, MI, 48109, USA
3 - Real Jardín Botánico, Plaza de Murillo 2, Madrid, 28014, Spain
Euphorbia subg. Esula
Presentation Type: Oral Paper:Papers for Sections
Location: Franklin B/Hyatt
Date: Tuesday, July 10th, 2012
Time: 9:00 AM