Good call, Mary. It is Ranunculus testiculatus, also known as Ceratocephalus testiculatus, Bur Buttercup. In the eastern U.S. it grows almost exclusively in campgrounds. It is new to Gray's Manual of Botany by M. L. Fernald.
This plant is unusual in that each pistil is scrotiform (that's a botanical term) at the base, having twin protuberances that look like testicles. Hence the specific epithet testiculatus, and the unofficial common name, Ballswort! It is not, however, related to Nut Rush or Nut Sedge.