Systematics Section / ASPT
Kim, Seung-Chul , Lee, Chunghee , Mejias, Jose A. .
Phylogenetic analysis of chloroplast matK gene and ITS of nrDNA sequences reveals polyphyly of the genus Sonchus (Asteraceae: Cichorieae).
THE genus Sonchus includes approximately 60 species occurring widely in Europe, Africa, Asia, Australia, the Mediterranean Basin, North America, and the Macronesian Islands. Sonchus is subdivided into three subgenera: Sonchus, Dendrosonchus, and Origosonchus. In this study, monophyly of the genus, as well as that of the three subgenera and respective sections, were tested based on ITS and matK gene sequences. In addition, several previously unknown phylogenetic relationships were determined. The results suggest that the genus is highly polyphyletic, and that only one of the three subgenera, Origosonchus, is monophyletic. Section Pustulati is only monophyletic in sections of genus Sonchus. A pattern which emerges from this study is that all Pacific and Atlantic island endemics, including the subtribe Dendroseridinae (Dendroseris and Thamnoseris), evolved within the Sonchus group. A high level of incongruence is observed between the ITS and matK topologies, and it is suggested that chloroplast DNA introgression via hybridization appears to be primarily responsible. Polyploidizaiton has played an important role in the evolutionary differentiation and speciation of the subgenus Sonchus, while other processes seem to better explain the speciation of the other two subgenera, Dendrosonchus and Origosonchus. The highly polyphyletic nature of this genus and the mutually independent evolution of several Pacific and Atlantic Island endemic genera within the Sonchus group both strongly suggest a need for a re-conceptualization and new delimitation of the genus Sonchus. We identified eight major clades, excluding Reichardia and Launaea, in the subtribe Sonchinae, and strongly advocate for their recognition as either (1) distinct genera, or (2) as closely related segregates. The latter alternative lends itself to the amalgamation of the disparate clades, including Dendroseris and Thamnoseris, into a single genus, Sonchus. Evaluation of morphological characters and phylogeny-based classification of the subtribe Sonchinae will be discussed.
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1 - University of California Riverside, Department of Botany & Plant Sciences, Riverside, California, 92521-0124, USA
2 - Sung Kwan University, Department of Biological Sciences, Suwon, , South Korea
3 - University of Seville, Department De Biología Vegetal Y Ecologia, Aptdo 1095, Sevilla, E-41080, Spain
Presentation Type: Oral Paper:Papers for Sections
Date: Wednesday, August 2nd, 2006
Time: 2:15 PM