Systematics Section / ASPT
Yang, Ya , Berry, Paul E. .
Phylogenetics and evolution of Euphorbia subgenus Chamaesyce (Euphorbiaceae).
Euphorbia subgenus Chamaesyce represents a distinct and monophyletic lineage within the giant genus Euphorbia s.l. It contains around 300 species of cosmopolitan distribution, but with its greatest diversity and likely origin in the desert region of northern Mexico and the southwestern U.S. It has many unusual synapomorphies including an independent origin of C4 photosynthesis; opposite, unequal-based leaves; interpetiolar stipules; a branching pattern resembling the inflorescence structure of some other Euphorbia species; and the suppression of a putative vegetative growth stage resulting in a shortened life cycle. The shift in flowering time and branching pattern, prevalence of annual and herbaceous habit, together with the origin of C4 photosynthesis could have contributed to the widespread adaptation of Chamaesyce to arid, exposed, high-temperature, disturbed, and nutrient-poor environments, starting with its origin and diversification during the formation of North American warm desert, and subsequent colonization of different habitat types around the world. Phylogenetic analysis of 60 Chamaesyce species from North America and all other continents using ITS and chloroplast spacers is presented. Monophyly of subgenus Chamaesyce is recovered, with the only known C3 lineage, subsect. Acutae, forming the sister group to the rest of the subgenus. All lineages outside of North America are deeply nested within North American clades, supporting a North American origin of Chamaesyce. Patterns of subsequent colonization in the Caribbean, Hawaiian Islands, Africa and South America are also discussed, among which the most noticeable is the Hawaiian radiation, with an reversal to woodiness in the 15 native Hawaiian Chamaesyce species.
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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, Department of Ecology & Evolutionary Biology, 830 North University Avenue, Ann Arbor, Michigan, 48109-1048, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Stevens 3/Hilton
Date: Wednesday, July 11th, 2007
Time: 11:30 AM