XVI International Botanical Congess
S.J. Brunsfeld and T.M. Hardig, Dept. of For. Res., Univ. of Idaho, Moscow, ID 83843. Hybridization is a common evolutionary process in North American Salix, often resulting in intraspecific cpDNA polymorphism. While exploring the broader, rangewide consequences of hybridization and introgression between S. sericea and S. eriocephala (subg. Vetrix), we discovered that both species, and at least four others, are polymorphic for a divergent cpDNA haplotype apparently acquired via hybridization with a member of subg. Salix. Frequency differences and differentiation within the various cpDNAs suggest: 1) multiple episodes of hybridization, probably both ancient and recent, 2) population contraction into at least two refugia at different times, and 3) complex phylogeographic patterns of dispersal and intermingling of cpDNAs.