Woody herb to 2 m high. Stems several to many, hairy to hairless; each stem persisting for 1 or 2 years. Leaves opposite each other, mostly 5–20 cm long, 12–50 mm wide, margins toothed. Flowers white or pale lilac or pale blue, sometimes pinkish outside or on buds, tubular, the tube 5–9 mm long, with 4 spreading lobes each to 8 mm long. Stamens 2. Flower clusters mostly 8–25 cm long, 40–100-flowered. Flowering: spring-summer.