nrDNA internal and external transcribed spacer sequences for investigating the systematics of Dieteria

The objectives of this research were to assess variation in nrDNA internal and external transcribed spacer (ITS and ETS) sequences of the morphologically diverse genus Dieteria and to determine how well the results of phylogenetic analysis corresponded with morphological variation, taxonomy, and geographic distribution. The first of two analyses included 39 samples from throughout the range of the genus representing 13 of the 16 currently accepted varieties, with ITS and ETS sequences combined to obtain the greatest resolution possible. This analysis produced phylogenies containing three major clades. One of the three consisted of samples from Washington, Oregon, and northern California. The second one included samples from southern California and western Arizona, plus additional ones from northern California, northern Nevada, and southeastern Idaho. The third clade was the largest and consisted of samples from the remaining part of the distribution of Dieteria. Comparison of the results with current taxonomy and morphological characteristics showed little correspondence between the molecular phylogeny and either taxonomy or morphology, suggesting multiple occurrences of convergent evolution. There were some correlations with geographic distributions. Except for the second and third clades’ distributions overlapping in some areas, the distributions of the three were mostly distinct from one another; smaller clades within them were also correlated with distributions. The second analysis included cloned sequences of five additional samples that were shown by initial sequencing efforts to contain many polymorphic nucleotide positions. In the results, the ITS and/or ETS for all five samples were placed in multiple positions some distance apart, indicating that these samples obtained their ITS and/or ETS sequences from distantly related ancestors through hybridization between members of two of the three major clades.