Dieteria occupies most of the western half of the United States, and extends short distances into Canada and Mexico. The genus is marked by substantial variation in morphological characters, notably leaf morphology, leaf and stem vestiture, and a number of phyllary characteristics such as size, shape, vestiture, and orientation of the herbaceous apices. This morphological variation has led to more than 50 species names having been proposed. The most recent complete treatment of Dieteria by B. L. Turner divided it into three species and 16 varieties: D. asteroides (3 varieties), D. bigelovii (3 varieties), and D. canescens (10 varieties). The objectives of this research were to assess variation in nrDNA ITS and ETS sequences, to see if phylogenetic analysis of this variation could help identify well-supported groups of taxa within the genus, and to determine how well these results corresponded with morphological variation, taxonomy, and geographic distribution. We started with ITS and ETS sequence data from 35 samples representing a large part of the distribution of Dieteria, and also representing 13 of Turner’s 16 varieties. Phylogenetic analyses produced phylogenies containing three relatively well supported major clades. Comparison of these results with morphological characteristics and with Turner’s taxonomy showed little correspondence between the molecular results and either morphology or taxonomy. On the other hand, there was substantial correspondence with geographic distribution. One of the three major clades consisted entirely 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. Except for the second and third clades’ distributions overlapping in Nevada and eastern California, the distributions of the three were mostly distinct from one another. A number of samples were not included in the initial analyses because their sequences contained polymorphic nucleotide positions. Several of these had been collected in areas where two of the three major clades neared one another or overlapped, suggesting that these samples may represent intergradation between the major clades. They are being investigated further by cloning and sequencing their ITS and ETS.