Virgin's Bower,  Clematis virginiana
Ranunculaceae or Buttercup Family

Sprawling, clambering vine with clusters of pure white flowers having 4 petals (actually sepals) and many stamens.  The leaves have 3 coarsely-toothed leaflets and come in pairs.  Fruit is a distinctive cluster of seeds with long hairy tails, sometimes called an old man's beard. Blooms in mid to late summer.

Native of open sunny, moist thickets, growing over other plants.  Common in the Park, especially under the powerline.  Also occurs as a weed in many people's yards.

Leatherflower (C viorna) has similar fruits and somewhat similar, although usually untoothed, leaves, but the flowers are very different, and it blooms in the spring to early summer.