Genetic variation within and among populations of Solidago riddellii (Asteraceae) was assessed using allozyme polymorphism to investigate the consequences of rapid migration of plant species on population genetic structure in this species. Riddell's goldenrod is an outcrossing, clonal herbaceous perennial species with a localized but widespread distribution. It occurs in fens and wet meadows with a global range from northern Arkansas through the upper Midwest with eastern extensions into Ontario, Canada and western populations known from southern Manitoba, Canada. Modern distribution is influenced by colonization northward following the retreat of Pleistocene glaciers in the upper Midwest and the fragmentation of wetland habitat by modern land use patterns. Accessions from 49 populations, with a total of 507 individuals, were analyzed for 9 enzyme systems coding for 23 putative loci. Four enzyme systems were polymorphic, with 5 monomorphic systems identified. Nei's genetic identity coefficient for the species overall was 0.93. The allozyme data does not support significant differentiation between eastern and western populations, nor does it support differentiation between northern and southern populations.

Key words: allozyme diversity, Asteraceae, rapid migration, Solidago riddellii