Spiraea virginiana is a federally listed rhizomatous shrub endemic to the southern Blue Ridge and Appalachian Plateau Provinces. The typical habitat of S. virginiana is along scoured sections of high gradient streams. No viable seeds or seedlings have been found in the wild, suggesting that populations within drainages are products of vegetative reproduction, most probably occurring when rhizomes broken loose from upstream populations wash downstream to form new ramets. There is considerable confusion, therefore, regarding identification of individuals and thus no known mechanism for evaluating population size and structure. Phenotypic variation in S. virginiana was investigated through a morphometric examination of leaf size and shape, using Morphosys to make 25 leaf measurements. These data were analyzed using Principal Components Analysis, to identify any morphological variation within and between drainages. We are currently examining genetic identity across the distribution using Randomly Amplified Polymorphic DNA (RAPDs), in an attempt to evaluate the genetic diversity. Genetic uniformity among the drainages would suggest that either extant populations are the ancestors of migrants that persisted through the glacial maximum in the watershed of the Gulf of Mexico, or are the products of a severe bottleneck during the Hypsithermal Period. Genetic variation among the drainages would suggest that S. virginiana persisted through the last glacial maximum within the present day drainage systems, supporting Ogle's hypothesis that the present distribution of S. virginiana represents the remnants of a more widespread distribution in the past. The RAPD data generally show genetic uniformity within drainages, suggesting that vegetative reproduction via dislodging of rhizomes during flooding is the predominant means of dispersal. The morphometric and RAPD data suggest that the northern part of the range exhibits greater variation than the middle and southern portion of the range, supporting OgleÕs hypothesis.

Key words: clonal growth, intraspecific genetic variation, morphometrics, Pleistocene migrations, RAPDs, Spiraea virginiana