High levels of allozyme variation within Cypripedium calceolus (Orchidaceae) and low levels of divergence among its varieties

An electrophoretic analysis of 12 isozyme loci was completed to determine the level of genetic variation within and degree of genetic divergence among populations of Cypripedium calceolus var. pubescens, C. calceolus var. parviflorum, and C. calceolus var. planipetalum. In addition, the genetic relationship between mixed and pure populations of vars. pubescens and parviflorum was determined. Differences were found among pure populations of these taxa in the level of heterozygosity and distribution of genetic variation. Variety-level heterozygosity over all loci ranged from 0.180 in var. pubescens to 0.274 in var. parviflorum, whereas the proportion of variation distributed among populations ranged from 5.3% in var. planipetalum to 17% in var. parviflorum. Only slight levels of genetic divergence were found among these taxa, which resulted from allele frequency differences among the varieties rather than the presence of high frequency taxon-specific alleles. Unweighted pair-group method analysis of Nei's genetic identities and a principal components analysis of allele frequencies both revealed a tendency of var. pubescens and var. planipetalum populations to cluster with their respective varieties. However, var. parviflorum displayed a large variance in population differentiation relative to the above taxa. Intravarietal Nei's identity values, which ranged from 0.84 to 1.0, were not consistently higher than intervarietal values (0.75-0.98). These results are comparable to other reports of genetic divergence among sympatric infraspecific taxa and suggest that vars. parviflorum, pubescens, and planipetalum be considered members of a single species