is often found growing in sandstone bedrock, gravel bars, nooks between boulders, and in riverborne deposits of debris, rubble, and silt. It is adapted to periodic flooding, scouring, erosion, and deposition of litter. Other plants in the habitat may include hazel alder (Alnus serrulata), silky dogwood (Cornus amomum), jewelweed (Impatiens capensis), creepers (Parthenocissus), ninebark (Physocarpus opulifolius), sycamore species (Platanus), blackberries (Rubus), willow species (Salix), American elderberry (Sambucus canadensis), soapworts (Saponaria), greenbrier species (Smilax), goldenrod species (Solidago), and poison ivy (Toxicodendron radicans). The plant is threatened by its small numbers, alterations in the hydrology of its riparian habitat, and habitat fragmentation. Populations are isolated from one another, reducing the frequency of its rare sexual reproduction even further. Populations are small; though the plant is adapted to a regime of flooding, unusually large floods have the potential to wipe out small populations. The invasion of introduced plant species, including the shrub's relative, Spiraea japonica (Japanese spiraea), may be a threat because of competition. References virginiana