A phylogenetic analysis of western North American Draba (Brassicaceae) based on nuclear ribosomal DNA sequences from the ITS region

To clarify relationships among western North American members of the genus Draba, we produced a molecular phylogeny using nucleotide sequences from both internal transcribed spacers of nuclear ribosomal DNA and the 5.8S rRNA gene (collectively, ITS). Sequence data from 17 Draba taxa and two outgroups were subjected to both parsimony and maximum likelihood analyses. The phylogenetic results support previously proposed informal groupings for the sampled species. Western North American Draba are divided into two well-supported clades: 1) all taxa with a chromosome number based on x = 8, and 2) taxa whose chromosome base numbers appear to be aneuploid, deviating from x = 8. The resulting phylogenetic framework also reveals the taxonomic limitations of flower color, chromosome base number, and growth habit for predicting relationships within the genus.