ITS sequences and phylogenetic relationships in Bidens and Coreopsis (Asteraceae)

Sequences from the internal transcribed spacer region of nuclear ribosomal DNA (ITS) for 35 taxa of Coreopsis and 15 species of Bidens were used to hy pothesize phylogenetic relationships within and between the two genera. Cor eopsis is paraphyletic and Bidens is polyphyletic in all most parsimonious trees. The ITS phylogeny indicates that the Bidens-Coreopsis complex origin ated in Mexico with subsequent primary radiations to North and South Americ a. The molecular data suggest that Bidens as now recognized has been derive d twice within Coreopsis, with one lineage tropical-subtropical and the oth er north temperate. These two lineages of Bidens are more widely dispersed, more species rich, and more morphologically diverse than any lineage of Co reopsis. The ITS phylogeny contains two major groups of North American Core opsis with one consisting of sections from Mexico and California and a seco nd comprised of eastern North American sections. These are the same two maj or groups recognized by morphology and/or cpDNA restriction site mutations. In most instances, sections of North American Coreopsis resolved as monoph yletic groups with morphology and/or cpDNA restriction sites also appear mo nophyletic in the ITS phylogeny. Coreopsis sect. Pseudoagarista is not mono phyletic because species from Mexico and South America appear in two differ ent strongly supported clades. Results of the present study indicate that e ventually taxonomic changes will be needed to reflect more accurately relat ionships in the Bidens-Coreopsis complex.