On the Bunchberry, the four large white bracts are easily mistaken for petals. However as a close look shows, they have no floral parts of their own, but surround a cluster of tiny true flowers.
Bunchberry, Cornus canadensis
False bugbane or Tassel Rue, a highly poisonous member of the Buttercup family has unusual flowers because they have tiny sepals and no petals; their showiness is a result of tufts of white stamens.