This native perennial plant is up to 3' tall, branching occasionally from the lower half of the central stem. This central stem is strongly winged and hairless. The leaves are alternate in the upper half of the central stem and opposite from each other in the lower half; they are usually alternate in the smaller side stems. The leaves are up to 4" long and 2" across, becoming gradually smaller as they ascend the stems. They are hairless, cordate or lanceolate, and have smooth margins. The inflorescence consists of a tall narrow spike up to 1½' long. One or two flowers appear from the axils of small leaves, which are crowded together along the spike. Each flower is about ½" across or slightly larger, and is lavender or purple. It has six lobes that flare outward from a tubular calyx; each lobe has a fine line of darker purple that leads to the throat of the flower. There are 6 stamens and a pistil that may, or may not, be exerted from the flower. The calyx is green or purple, with six triangular teeth. The blooming period occurs from mid- to late summer, and lasts about 1-2 months. There is no floral scent. The root system consists of a taproot with rhizomes. The tiny seeds can be carried a considerable distance by wind or water.