Spiraea virginiana Britton (Virginia spiraea), an endangered riparian shrub found in the Appalachian and Blue Ridge Mountains, reproduces primarily via asexual reproduction. Sexual reproduction is rare under natural conditions, but it is unclear whether pollen limitation or genetic incompatibilities are the underlying cause. Open, selfed, inbred, and outbred pollination treatments were applied to populations of S. virginiana in three Western North Carolina counties. In addition, stigmas from open pollinated treatments were collected to quantify pollen loads. Flowers from pollination treatments were collected 90-120 days later, and a subset of seeds were stratified for three months before testing germination rates. In addition, 100 seeds from each replicate were tested for viability using TTC. Both foreign and conspecific pollen loads on Graham County stigmas were significantly lower (P = 0.0001) than pollen loads on stigmas from other populations. Seed set from Ashe County plants was significantly lower than other populations (P = 0.0001), but treatment had no significant effect on seed set (P=018). Because seed set was not correlated with pollen load, variation in reproductive success could be due to other factors. We are currently investigating genetic variation within and among populations to see if that could explain differential seed production.
