Habitat fragmentation has become an important concern in the midwestern United States due to conversion of temperate deciduous forests to agricultural land during the past two centuries. The genetic effect of forest fragmentation in these areas was examined in a common understory herb, Viola pubescens, a species that produces self-pollinated cleistogamous (CL) flowers and potentially outcrossing chasmogamous (CH) flowers. Using allozymes, genetic variation was measured in populations inhabiting woodlots of differing sizes (0.5 - 40.5 ha) and distances from one another (0.3 - 11.4 km) within the agricultural landscape of central Ohio. Woodlot size was significantly and positively correlated with all measures of genetic variation (A, P, Ho, and He), with variation highest in the larger woodlot populations (e.g., P = 0.88, Ho = 0.39) and lowest in the smaller woodlots (P = 0.25, Ho = 0.03). Overall, populations were genetically differentiated from one another (q = 0.34), but there was no relationship between genetic and geographic distance. More likely, limited gene flow in this species may reflect a reduction in pollinators in the fragmented woodlots, leading to an increase in selfing rates through automatic selfing in CL flowers and delayed selfing in CH flowers. Despite the commonality of V. pubescens and the reproductive advantage it has through the CH/CL system, fragmented populations still experience genetic erosion. This study highlights the need for conserving the remaining populations of this species, along with other less common taxa in the temperate deciduous forest.

Key words: cleistogamy, genetic effects, habitat fragmentation, Viola pubescens