Phylogeographic patterns and high levels of chloroplast DNA diversity in four Packera (Asteraceae) species in southwestern Alberta

Chloroplast DNA (cpDNA) haplotype variation is compared among alpine and pr airie/montane species of Packera from a region in southwestern Alberta that straddles the boundary of Pleistocene glaciation. The phylogeny of the 15 haplotypes identified reveals the presence of two groups: one generally fou nd in coastal and northern species and the other from species in drier habi tats. The presence of both groups in all four species and most populations from southwestern Alberta is evidence of past hybridization involving speci es or lineages that may no longer be present in the region. With the except ion of the alpine P. subnuda (Phi (ST) = 1.0), interpopulational subdivisio n of haplotype variation is low (Phi (ST) < 0.350), suggesting that interpo pulational gene flow is high. However, based on haplotype distribution patt erns, we propose that Pleistocene hybridization and incomplete lineage sort ing have resulted in reduced subdivision of interpopulational variation so that gene flow may not be as high as indicated. Drift has been more importa nt in the alpine species populations, especially P. subnuda.