Allozyme and morphological analyses were conducted to test speculation and recently published taxonomy concerning northern versus southern variation in the Cypripedium parviflorum complex. Allozyme analyses of 40 populations from 10 states revealed marked differences in genetic variation between northern and southern populations of var. pubescens, and between var. makasin and var. parviflorum. For both comparisons, the northern populations from previously glaciated regions generally contain more genetic variation and larger estimated population sizes than do their southern counterparts. These results are in contrast to most published findings on other taxa that report higher levels of genetic variation in populations near glacial refugia compared to conspecifics from previously glaciated territory. To explain the data in our paper, we suggest the existence of a northern refugium for C. parviflorum in a periglacial environment that contained abundant habitat for this species. This region could have served as a genetically diverse source of propagules for colonizing newly deglaciated territory. Conversely, populations in the heavily forested south may have remained relatively small and isolated throughout glaciation, promoting genetic drift and the loss of genetic variation. Lastly, var. makasin differs from the other two varieties in mottling and coloration of the dorsal sepal, and in pubescence on the uppermost, nonphotosynthetic sheathing leaf. These data are consistent with previous hypotheses of northern versus southern differentiation in C. parviflorum, and support recognition of newly restored var. makasin.

Communicating Editor: Jeff H. Rettig