A coarse perennial herb from tropical America in the same family as Lantana. Usually 8-20 cm tall, sometimes woody toward base. Stems usually weakly erect. Leaves opposite, 4-8 cm long, upper surface rough, margins serrate. Tubed flowers usually dark purplish blue with a paler centre, the tube 7-8 mm long. Fruit a nutlet in a drupe, enclosed by a persistent calyx.
A common weed in moist, fertile, disturbed soi. Invades forests and pastures in medium wet to wet areas often forming dense stands, in lower densities in dry area. Usually planted intentionally as ornamentals then spread by the movement of garden soil and by rainwater.
Photo: Craig W.