Spiraea virginiana Britton is an imperiled rhizomatous shrub endemic to the southern Blue Ridge and Appalachian Plateau physiographic provinces. It is Federally listed as Threatened. Populations of S. virginiana are restricted to scoured sections of high gradient streams within the Ohio River drainage. Present evidence indicates that the species is reproducing asexually, most probably through the deposition of rhizomes from upstream populations forming new downstream ramets, across most of the range. This lack of sexual reproduction suggests that the populations have undergone bottlenecks in most of the drainages. Our previous work examined phenotypic variation through a morphometric evaluation of 25 leaf measurements and showed considerable divergence of leaf shape in the Ohio, Cumberland, and Tennessee River drainages. Randomly Amplified Polymorphic DNA (RAPDs) were used to construct a scenario of past gene flow. The current study reports on the use of trnL chloroplast sequence data and Inter-Simple Sequence Repeats (ISSR) variation to test conclusions reached in the previous study. The combined results support the conclusion that there is a greater degree of relatedness along short reaches of a single river than within a secondary drainage basin. Results place the S. virginiana ancestral populations in the southern part of its range suggesting a southward migration followed by recolonization northward during the last glaciation, concordant with the work of Delcourt and Delcourt (1981, 1984). Biogeographical patterns of variation within S. virginiana identify the Cumberland Plateau as a probable migratory route. In addition, evidence suggests that the deeply dissected Cumberland Plateau is the probable site of a Pleistocene refugium.

Key words: Cumberland Plateau, ISSR, Pleistocene refugium, RAPD, Spiraea virginiana, trnL