Phylogenetic relationships of eastern North American Phlox L. are complicated, and many studies have suggested this may be due in part to hybridization. Recently developed molecular phylogenies (based on markers from the nuclear and chloroplast genomes) showed patterns of incongruence consistent with hypotheses of hybridization, although other causes of incongruence were not ruled out. To explore the potential evolutionary role of hybridization in Phlox, we are investigating genetic relationships and variation in populations of two species, P. pilosa L. and P. divaricata L., in and near the Ozark highlands of the central United States. Phlox pilosa exhibits striking morphological variation in the Ozarks, and a distinct subspecies is recognized, P. pilosa subsp. ozarkana (Wherry) Wherry. Given that P. pilosa and P. divaricata occasionally come into local contact and hybridize, it is intriguing to ask whether introgression has occurred between these species in the Ozark region, potentially contributing to the variation observed within P. pilosa. A phylogeographic approach to this question is presented, and preliminary gene trees based on regions of low-copy number nuclear genes are discussed, along with some of the challenges of developing and interpreting these trees. In addition, development of microsatellite markers is underway, and these methods are outlined. The microsatellite data will yield information on population genetic structure for comparison with the gene genealogies. Overall, this approach of carefully examining genetic data at the population level and interpreting that information within a larger phylogenetic context will provide insights that lead to an improved understanding of the evolutionary processes at play in Phlox.

Key words: hybridization, introgression, Phlox divaricata, Phlox pilosa, Polemoniaceae