Yang, Ya , Berry, Paul E. .
Evolution of weediness in the Chamaesyce clade of Euphorbia s.l. (Euphorbiaceae) – biogeography, shift to early onset of reproductive growth, and opportunistic life-history strategies.
The Chamaesyce clade of Euphorbia s.l. (Euphorbiaceae) contains 250–300 species and is distributed worldwide. Many of them are common weedy species such as Euphorbia maculata, E. prostrata, and E. thymifolia. Ongoing range expansions of weedy species, especially in Eurasia, have been reported numerous times in the recent years. Some characters that distinguish Chamaesyce from most Euphorbia are related to their quick growth and an opportunistic life-history strategy, including the transition from C3 to C4 photosynthesis and the evolution of a sticky seed coat. Of particular interest are the putatively highly suppressed vegetative growth stage and a shift toward early onset of the reproductive stage, which result in continuous flowering and mass seed production. A molecular phylogeny of nuclear ITS and chloroplast rpl16, trnL-F and trnH-psbA from 120 Chamaesyce species recovers three main clades: 1) a basal clade sister to the rest,Â which includes three non-weedy perennial species restricted to the Chihuahuan Desert in North America; 2) a non-weedy clade mostly restricted to Southern US and Mexico; and 3) sister to it a primarily weedy clade with all the weedy species nested in it. This weedy clade also contains a large number of narrow endemics found in a variety of habitats worldwide, including 11 federal-listed endangered or threatened species in the US. Based on the molecular phylogeny and morphological studies, the following hypotheses are tested: a) annual habit and self-pollination are associated with weediness and long-distance dispersal; b) the sticky seed coat evolved within Chamaesyce, and was lost multiple times in narrowly endemic species; and c) by early abortion or lack of activity in the apical meristem of the main axis, lateral branches emerging from below the apex of the main axis are homologous to the reproductive branches in other Euphorbia.
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1 - University of Michigan, Ecology and Evolutionary Biology, 2037 Kraus Natural Science Building, 830 North University Ave., Ann Arbor, MI, 48109-1048, United States
2 - University of Michigan, EEB Department and Herbarium, 830 N University, Ann Arbor, MI, 48105, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Council Chambers/SUB
Date: Monday, July 28th, 2008
Time: 2:30 PM