Variation among the Aureoid Senecios of North America: A geohistorical interpretation

Phylogeographic Patterns and High Levels of Chloroplast Dna Diversity in Four Packera (Asteraceae) Species in Southwestern Alberta

“…Yates et al (1999) explained the high haplotype (Barkley 1978;Moss 1983), the species is unlikely to have survived glaciation in northern refugia such as AlaskaYukon and then migrated south in the postglacial interval. We think it more likely that, as northern Packera species were pushed south by advancing ice during the Pleistocene, they hybridized with northern P. pseudaurea populations and that the resultant polymorphic populations (e.g., RR, CL) survived in an ice-free region or regions in southwestern Alberta between Laurentide and Cordilleran glaciers.…”

“…Although the four Packera species exhibit morphological and ecological differences that allow their identification in the field (Barkley 1978;Moss 1983;Whitton and Bain 1992), the discriminant analysis of cpDNA haplotype frequency data from populations in southwestern Alberta region failed to detect any significant differences among them (Fig. 5).…”

“…Two well-known indicators of biogeographic disturbance, introgression and hybridization, are thought to be common within Packera (ϭ aureoid Senecio complex) based on numerous studies of morphology, chemotaxonomy, and cytotaxonomy (Barkley 1962(Barkley , 1978(Barkley , 1988Kowal 1975;Bain and Denford 1985;Bain 1988). All of these studies suggest that glaciation has been important in shaping the evolution of the genus.…”

“…Packera subnuda, the other alpine species, is at the northernmost limit of its range (Barkley 1978), whereas P. pseudaurea and P. cana extend as far north as central Alberta as well as further south and east. Bain and Jansen (1996) found no evidence of intrapopulational haplotype var- Table 2.…”

A Phylogeny of Packera (Senecioneae; Asteraceae) Based on Internal Transcribed Spacer Region Sequence Data and a Broad Sampling of Outgroups

“…Barkley (1988) provided a detailed discussion of the geohistory of the complex, concluding that historical events such as glaciation had played a major role in the evolution of the genus by creating opportunities for widespread hybridization, an opinion shared by other authors (e.g., Kowal, 1975;Bain, 1988). More recently, Bain and Jansen (1996) found unusually high levels of intrapopulational cpDNA polymorphism within many species and populations from throughout the range of Packera, supporting the notion that widespread past and perhaps ongoing introgression has occurred.…”