ITS Sequences and Phylogenetic Relationships in Bidens and Coreopsis (Asteraceae)

Abstract

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 hypothesize phylogenetic relationships within and between the two genera. Coreopsis is paraphyletic and Bidens is polyphyletic in all most parsimonious trees. The ITS phylogeny indicates that the Bidens-Coreopsis complex originated in Mexico with subsequent primary radiations to North and South America. The molecular data suggest that Bidens as now recognized has been derived twice within Coreopsis, with one lineage tropical-subtropical and the other north temperate. These two lineages of Bidens are more widely dispersed, more species rich, and more morphologically diverse than any lineage of Coreopsis. The ITS phylogeny contains two major groups of North American Coreopsis with one consisting of sections from Mexico and California and a second comprised of eastern North American sections. These are the same two major groups recognized by morphology and/or cpDNA restriction site mutations. In most instances, sections of North American Coreopsis resolved as monophyletic groups with morphology and/or cpDNA restriction sites also appear monophyletic in the ITS phylogeny. Coreopsis sect. Pseudoagarista is not monophyletic because species from Mexico and South America appear in two different strongly supported clades. Results of the present study indicate that eventually taxonomic changes will be needed to reflect more accurately relationships in the Bidens-Coreopsis complex.