The Trillium pusillum Michaux (Liliaceae) Complex in Virginia. II. Isozyme Evidence

Electrophoresis of isozymes was carried out on samples from six populations of Trillium pusillum Michaux from the mountains and coastal plain of Virginia; samples of T. pusillum var. ozarkanum from Arkansas and T. pusillum from Alabama were also included for comparison. Twelve loci from nine enzyme systems were found to be consistently decipherable; of these, eight were polymorphic. The mean expected heterozygosity (H,) for all populations was 0.140. Chi-square analysis of genotype frequencies and calculated values of Wright’s Fst were consistent with an outcrossing breeding system with near random mating within each population, a result also suggested by studies of pollination using pollinator exclosures. The mean value for Wright’s Fst was calculated to be 0.414, indicating extensive population differentiation. The gene flow parameter, Nm, was estimated from Fst to be 0.354, suggesting a low level of gene flow among populations. This is consistent with what is known of pollination and seed dispersal. No compelling evidence was found for separate varietal status for the mountain populations from Virginia, and it is recommended that all Virginia populations be considered a single variety.