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Abstract Detail

Systematics Section

Horn, James W. [1], Van Ee, Benjamin [2], Morawetz, Jeffery J. [3], Riina, Ricarda [4], Berry, Paul E. [5], Steinmann, Victor W. [6], Wurdack, Kenneth [7].

Phylogeny and evolution of growth forms in the giant genus Euphorbia (Euphorbiaceae).

Euphorbia, with over 2100 recognized species, is the second-largest genus of angiosperms. Beyond mere species richness, one of the most impressive aspects of the evolutionary biology of Euphorbia is its extensive diversification of growth forms (physiognomies), which include annual herbs, large trees, semi-succulent “pencil plants,” and an extensive array of cactiform, caudiciform, and geophytic xerophytes. As a major goal of the Euphorbia Planetary Biodiversity Inventory (PBI) project, a robust, global phylogeny of Euphorbia was reconstructed to address evolutionary questions, as well as to provide the framework for future phylogenetic studies and an updated classification of this complex genus. To achieve this, we sequenced 9 loci (~16 kb for each taxon), from all three genomic compartments (cp: ndhF, rbcL, rbcL-accD, rpl16, trnL-F; mt: nad1B-C, rps3; nu: exons 9 & 12 of EMB2765, ITS) for 155 species of Euphorbia and 15 outgroup genera. Parsimony, maximum likelihood, and Bayesian analyses all resolve the same backbone topology with strong support. In these phylogenies there are four major clades that are successively sister to each other, beginning with the currently recognized subgenera Esula (Clade B of previous studies), Rhizanthium (Clade A), Euphorbia (Clade C) and Chamaesyce (Clade D). The “pencil-plant” and caudiciform physiognomies are independently derived within each of these four major clades. Cactiform succulents are independently derived in subgenera Euphorbia and Rhizanthium, where each is associated with species-rich clades. Likewise, the evolution of annuals in Euphorbia, notably occurring within subgenera Esula and Chamaesyce, also appears to have promoted a high degree of speciation in clades associated with this trait. Although the origin of the cyathium is frequently implicated as a key innovation that enabled the adaptive radiation of Euphorbia, our results suggest that the recurrent evolution of varied, specialized growth forms is an additional factor important to the diversification of this giant genus.

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Related Links:
Euphorbia PBI Website

1 - Smithsonian Institution, Botany, National Museum of Natural History, MRC 0166, P.O. Box 37012, Washington, DC, 20013-7012, USA
2 - Harvard University, Arnold Arboretum, Harvard University Herbaria, 22 Divinity Avenue, Cambridge, MA, 02138, USA
3 - University of Michigan, Herbarium & Dept. Ecology and Evolutionary Biology, 3600 Varisty Drive, Ann Arbor, MI, 48108, USA
4 - University of Michigan, Herbarium and Dept. of Ecology and Evolutionary Biology, 3600 Varsity Dr., Ann Arbor, MI, 48108, USA
5 - University of Michigan Herbarium, Ecology and Evolutionary Biology, 3600 Varsity Dr, Ann Arbor, Michigan, 48108, USA
6 - Instituto de Ecología, A.C., Centro Regional del Bajío, Avenida Lázaro Cárdenas 253, Col. Centro, Pátzcuaro, Michoacán, 61600, Mexico
7 - Smithsonian Institution, Botany Department, PO Box 37012, NMNH, MRC-166, Washington, DC, 20013-7012, USA

character evolution
shoot morphology
molecular phylogeny.

Presentation Type: Oral Paper:Papers for BSA Sections
Session: 57
Location: Maybird/Cliff Lodge - Level C
Date: Wednesday, July 29th, 2009
Time: 10:45 AM
Number: 57010
Abstract ID:679