Identifying Evolutionary Significant Units in Spiraea virginiana

Spiraea virginiana Brit. (Rosaceae) is a rare clonal shrub found in isolated populations within the Cumberland, Tennessee, and Ohio River drainages. This species has been listed as federally endangered since June 1990 due to anthropogenically induced habitat loss and population fragmentation as a result of river damming. Reproduction consists of a mixed mating system that is mostly asexual by ramet formation, with occasional dispersal via vegetative fragmentation downstream. Successful sexual reproduction is limited, and could result from self-fertilization or outcrossing. The species does appear to outcompete other shrub species by vigorous rhizome production and its ability to withstand scouring floods.The lack of sexual reproduction could potentially result in an extremely limited effective population size in each river. This study aims to assess the genetic diversity of S. virginiana populations along the New and Cheoah Rivers in North Carolina using eight previously published microsatellite markers. Our results suggest a small effective population size within each of the two rivers. These results are consistent with earlier investigations and could have management implications, possibly treating each river drainage as its own evolutionary significant unit for (ESU).