Annual or perennial herbs with entire, opposite leaves. Inflorescences of axillary heads or short spikes, bracteate. Flowers bisexual, solitary in the axil of each bract, subtended by 2 bracteoles. Tepals 5, glabrous and 1-nerved or barbed-pilose and 3-nerved, free, equal or unequal. Stamens 2-5, alternating with pseudostaminodes. Fruit an indehiscent capsule.