Genetic analyses can provide important insights for the successful reestablishment or augmentation of populations of endangered plant species. Tiedemannia canbyi (Apiaceae) is an endangered southeastern US coastal plain species whose natural range extends from southwestern Georgia to southeastern North Carolina with a disjunct (approximately 600 km) population in Maryland. T. canbyi currently has only approximately 40 known populations. Thirty nuclear allozyme loci were employed to determine the levels and distribution of neutral genetic diversity within and among 14 populations of T. canbyi and eight populations of its more common and widespread congener, T. filiformis. Both species exhibited relatively high levels of genetic diversity (H_e = 0.185 and 0.284 for T. canbyi and T. filiformis, respectively). The Maryland population of T. canbyi had the lowest overall level of genetic diversity (H_e = 0.089). Genetic differentiation among populations of both species was similar (G_ST = 0.250 and 0.254). Populations of T. canbyi formed two genetically distinct groups, southwest and south-central Georgia vs. eastern Georgia, South Carolina, and Maryland. Six T. filiformis populations from southern and coastal Georgia and coastal South Carolina formed one genetically similar group while an inland population from Georgia and an inland South Carolina population were genetically distinct from each other and from the six coastal populations. Patterns of genetic variation observed for these two Tiedemannia species are most consistent with the different groups of populations having originated from genetically discrete glacial refugia. The value of these results for the restoration and/ or augmentation of T. canbyi populations is discussed.