XVI International Botanical Congess
Herbarium and Dept. of Biological Sciences. In North America, Euphorbia subg. Esula sect. Esula includes ±24 species with greenish paired bracts subtending the cyathia and cornute cyathial glands. Seven N. American annual species are placed by Boissier together with species of the Old World. Hurasawa formally grouped these taxa together within a holarctic group--the Subsect. Foveospermae--comprising annuals or shortlived perennials with foveolate or pitted seeds. The monophyly of this group is being considered using ITS sequence data. At present, the data are unable to resolve relationships among the sampled taxa. Furthermore, North American species of Esulae and Foveospermae share large deletions not found in other species in the subgenus Esula. The implications of these data are discussed.