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Abstract Detail

Systematics Section/ASPT

Horn, James [1], Xi, Zhenxiang [2], Riina, Ricarda [3], Berry, Paul [4], Davis, Charles [5], Wurdack, Kenneth [6].

Evolutionary bursts in the Euphorbia (Euphorbiaceae) Tree of Life are linked with photosynthetic pathway.

Euphorbia includes ~2100 species and a staggering diversity of growth forms and alternative photosynthetic pathways. Its distinctive inflorescence "the cyathium" is a synapomorphy of the genus and has been proposed as a key innovation that may explain the exceptional diversity within this group. A competing hypothesis contends that Euphorbia diversification is much more recent and greatly post-dates the origin of this putative key innovation. We present a dated phylogeny of Euphorbia and Euphorbioideae outgroups using nine molecular markers (176 taxa, ~16 kbp per taxon), combined with information on standing taxonomic diversity to identify shifts in diversification within Euphorbia. The crown clade of Euphorbia is indeed more species-rich than expected by chance when compared with estimate of net species diversification from background rates of Euphorbiaceae. Further analyses focused on Euphorbioideae support at least nine increases in diversification within Euphorbia, with most of these occurring between ~5­-20 Ma. Five of the relatively recent radiations just mentioned are clades of CAM succulents that are endemic to Africa and Madagascar. Contemporaneous with these succulent radiations is the origin of the hyperdiverse C4 lineage of Euphorbia section Anisophyllum in the New World. In contrast with these diversification rate increases, the diversification rate at the base of the Euphorbia clade is not significantly different from the background rate of Euphorbioideae. Our results, therefore, favor a hypothesis of Euphorbia diversification as a series of relatively recent, exceptional radiations, which are frequently linked with transitions to alternative photosynthetic pathways.

Broader Impacts:

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Related Links:
Euphorbia Planetary Biodiversity Inventory

1 - Smithsonian Institution, Department Of Biology, MRC 166 PO Box 37012, Washington, DC, 20013-7012, USA
2 - Harvard University, Harvard Herbaria, Department of Organismic and Evolutionary Biology, 22 Divinity Ave., Cambridge, MA, 02138, USA
3 - Real Jardn Botnico, Plaza de Murillo 2, Madrid, 28014, Spain
4 - University Of Michigan, Department Of Ecology And Evolutionary Biology, 830 N UNIVERSITY ROOM 2035, Ann Arbor, MI, 48109, USA
5 - Harvard University, Department of Organismic and Evolutionary Biology, Harvard University Herbaria, 22 Divinity Avenue, Cambridge, MA, 02138, USA
6 - Smithsonian Institution, Botany, MRC-166 National Museum Of Natural History, National Museum Of Natural History, MRC 166, PO Box 37012, Washington, DC, 20013-7012, USA

CAM photosynthesis
C4 photosynthesis
divergence dates.

Presentation Type: Oral Paper:Papers for Sections
Session: 18
Location: Franklin A/Hyatt
Date: Monday, July 9th, 2012
Time: 1:30 PM
Number: 18001
Abstract ID:934

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