Knotweed Virginia/ Jumpseed
 

Tovara virginianum
The stem-joints of this 2-4' plant are swollen and covered by hairy sheaths. The alternate leaves are broad and often have a dark spot near the center of the upper surface. The upper part of the plant consists of a long, very slender spike of tiny greenish or rose-colored flowers. Blooms July-October in woods.

Upward pressure on the seed capsule causes the seed to "jump" up to several feet, accounting for the alternate name.