A large, hairy, clump-forming North American native perennial of wet meadows, low woods, stream banks, and prairies. Its most distinctive feature is the perfoliate foliage — pairs of wrinkled, opposite, lance-shaped leaves whose bases fuse around the hairy stem, so the stem appears to pass through the leaf. From July to September, flat-topped clusters of small, fluffy white flowers feed a wide range of bees, butterflies, and other pollinators, while all parts of the plant are toxic and bitter.