Annual or short-lived perennial prickly herb, 0.2–1 m tall, mostly branching from the base, with prickly stems and leaves due to tubercle-based prickles. Leaves are opposite, sometimes alternate in parts, elliptic, narrowed at both ends, about 5 cm long and 2.5 cm wide. Flowers are bluish with a yellow center, 6–12 mm across, and arranged in terminal and axillary panicles on long pedicels. Calyx is densely white-hairy, about 6 mm long, and enlarges in fruit to 10 mm long or more. Corolla lobes are ovate and long-acuminate. Flowers have five stamens with oblong to linear anthers, densely white-hairy, with naked appendage tips. Fruits are ovoid, brown nutlets, about 6 mm long, with dentate, prickly margins.