**Description:** A wetland wildflower with hairy stems and wrinkled, opposite leaves that appear to be "pierced" by the stem.
**Size:** 2 to 4 feet tall.
**Historical Use:** Named for its folk medicine use in treating "break-bone fever" (dengue); leaves were once used as bandages for fractures.
**Identification:** Features unique "perfoliate" leaves where the pair is fused around the stem. Produces flat-topped clusters of tiny white flowers in late summer.
**Habitat:** Wet meadows and silty banks of forest streams.