A single population of Pediomelum piedmontanum (Fabaceae) occurs in Columbia County, Georgia. We examined allozyme variation in this population for 20 loci in eleven enzyme systems. Genetic diversity was low (P = 20.0%; A = 1.20; overall average HO= 0.038). Allelic frequencies in a large sample from one of two subpopulations predicted a significant deficiency of heterozygotes for all polymorphic loci (P < 0.001), inconsistent with Hardy-Weinberg expectations. Allelic frequencies for a smaller sample from the other subpopulation predicted a significant deficiency of heterozygotes for one polymorphic locus (P < 0.025) and nonsignificant excesses of heterozygotes for two others. Genetic differentiation among subpopulations was low (FST = 0.0142). Factors responsible for the extreme rarity of P. piedmontanum are unknown, but low genetic variation in the small, isolated Georgia population is most likely due to historical factors, genetic drift, and perhaps inbreeding.

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