Morawetz, Jeffery J. , Riina, Ricarda , Berry, Paul E. .
Preliminary phylogeny of Euphorbia subg. Rhizanthium (Euphorbiaceae): An exclusively Old World lineage with amazing morphological diversity.
Recent molecular phylogenetic research on the giant genus Euphorbia has supported the recognition of four subgenera, each with unambiguous support for their monophyly. Here we present the first detailed hypothesis of relationships within the exclusively Old World subgenus Rhizanthium based on ITS and ndhF sequence data. With ca. 200 species, subgenus Rhizanthium contains a variety of growth forms, including herbaceous, geophytic, caudiciform, woody, and semi-succulent woody species. The greatest diversity is achieved among succulent taxa, including the morphologically well-characterized “medusoid” species. Here we support the placement of the woody E. antso, a Madagascan endemic, sister to the rest of subgenus Rhizanthium. The next diverging lineage is the Arabian dwarf caudiciform E. hadramautica. The remaining lineages contain groups of exclusively herbaceous, woody, or succulent species, with the largest clade representing the majority of diversity in succulence found within subgenus Rhizanthium. Despite the presence of morphologically cohesive groups of succulent species, branch lengths in the large succulent clade are surprisingly short, offering no resolution of relationships among these species. Our data support the placement of the spineless pencil-stemmed succulent species E. dregeana and E. larica within subgenus Rhizanthium, with this growth form now present in all four subgenera. These results support the hypothesis of rapid diversification and specialization within arid habitats of the Old World, which would result in the short branch lengths recovered for the succulent taxa. Arid radiations are not unique to subgenus Rhizanthium, as the large spine-shield group in subgenus Euphorbia shows a similar pattern of diversification in arid habitats.
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EuphORBia: A global inventory of the spurges
1 - Rancho Santa Ana Botanic Garden, 1500 N. College Ave, Claremont, California, 91711, USA
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: 3:30 PM