Phylogenetic Relationships among the Genera of the Subtribe Sonchinae (Asteraceae): Evidence from ITS Sequences

Sequences from the internal transcribed spacer region (ITS) of nuclear ribosomal DNA were used to assess relationships among genera of subtribe Sonchinae (Lactuceae). The data suggest that Sonchinae is paraphyletic, and that the Dendroseridinae should not be recognized as a distinct subtribe. Several Macaronesian genera, along with woody Macaronesian species of Sonchus (all diploid, 2n = 18), appear to have been derived from a common ancestor. Prenanthes pendula is more closely related to this Macaronesian group than to other members of Prenanthes, suggesting that Prenanthes, like Sonchus, is polyphyletic. The Juan Fernandez Islands endemic genus Dendroseris (2n = 36) is monophyletic, but its phylogenetic relationships to other Sonchinae remain uncertain. Reichardia, which forms the sister genus of the Sonchinae, is also monophyletic. Launaea, by contrast, is considered to be paraphyletic. The monotypic genus Aetheorhiza (2n = 18) is sister to the annual weedy species of Sonchus, rather than being closely related to Launaea. Two monotypic endemic genera from New Zealand, Embergeria (2n = 36) and Kirkianella (2n = 90, 126), are sister genera, and together they form the sister clade to Sonchus arvensis-S. maritimus. This implies that these Pacific genera were derived either from section Arvenses or Maritimi of subgenus Sonchus, rather than from section Apseri.