Herbs annual [or perennial]. Roots slender, fibrous. Sometimes with elongated rhizomes. Leaves opposite [or whorled]. Inflorescences terminal and axillary, in clusters or sometimes in lax panicles of cymes. Terminal clusters umbel-like, subtended by a whorl of 4 leaves, often on short axillary branches. Flowers 4merous. Calyx lobed nearly to base. Corolla campanulate, lobed to below middle, with spurs near base of corolla tube. Stamens inserted on corolla tube. Ovary 1celled. Style very short. Stigma 2lobed. Capsules ovoid, 2valved, 1.1-1.3 cm, many seeded. Seeds ellipsoid to subglobose; seed coat almost smooth.

About 100 species: mainly in America, a few species in Asia and Europe; two species in China.