A woody shrub, 2-3 feet tall. Opposite, toothed leaves. Four-petaled flowers with numerous stamens. Sepals almost as long as the petals. Overall shape and leaves look very much like some sort of Viburnum, but the flowers aren't at all Viburnum like.
Found in an old-growth forest adjacent to James and Dolley Madison's house in Montpelier, Virginia. It was fairly common along the trail I walked.
Even though I was in an old-growth forest, I was (a) near the edge of the forest, (b) on a path, and (c) very near to the Madison's garden. As such, it is possible that these shrubs escaped into the woods at some point. Should have gone into the garden to see if it was there, but I didn't have the chance.