- To +40cm tall, herbaceous, rooting at nodes below, from creeping rhizomes, glabrous, with seven distinct vascular bundles in a ring and one bundle in center of that ring when stem is cut in cross section.
- Opposite, sessile to very short-petiolate, linear to linear-elliptic or linear-lanceolate, to +10cm long, 2.5cm broad, glabrous, entire to shallow crenate.
- Axillary capitate pedunculate spikes to +/-3cm long. Peduncles to +10cm long. Flowers opposite.
- Corolla bilabiate, white to pale lavender or pale violet. Corolla tube 4-5mm long. Upper lip reflexed, bluish to purplish 6-7mm long, 5mm broad, notched at apex. Lower lip 3-lobed. Larger central lobe with purple mottling, 1cm long, 5mm broad. Lateral lobes spreading, 8mm long, 3mm broad, typically white. Stamens 2, adnate near apex of corolla tube, slightly exserted from upper lip. Filaments white, 5mm long, glabrous. Anthers with distinct sacs, purplish to brownish. Ovary green, glabrous, 1.2mm long, conic. Style white, glabrous, 9mm long. Calyx 5-lobed. Lobes to 6mm long, 1mm broad, glabrous, green, acute to acuminate, with lighter margins.
- May - October.
- Wet locations, typically in still water.
- Native to U.S.
- The plant forms large mats or colonies on the shoreline of lakes, ponds and streams. It is very common. Although the flowers have a tremendous amount of purplish tint, they still look whitish from a distance.
Photographs taken at the Kansas City Zoo, 6-13-00, and along the shores of the Current River, Shannon County, MO., 6-13-03.