Annual or perennial slender herbs. Leaves opposite, simple, entire, exstipulate. Flowers in dichasial cymes, rarely solitary. Sepals 5 (rarely 4), free, persistent. Petals 5 (rarely 4), usually 2-fid to 2-partite, sometimes 0. Stamens 10, rarely fewer or 0, hypogynous or perigynous, mostly inserted on an annular disk. Ovary 1-celled, many- or few-ovuled; styles (2-) 3 (-4). Capsule spherical or oblong, usually dehiscing by 6 valves. Seeds many, rounded-reniform, more or less compressed, papillose or echinulate.