Small shrubs [or herbs]. Leaves alternate, ± sessile; stipules in pairs, small; leaf blade narrowly elliptic to almost needle-shaped, margin entire to incised. Flowers axillary, bisexual, zygomorphic, solitary, with a pair of bracteoles at joint of peduncle and pedicel. Sepals persistent, ± triangular, nearly equal, margin entire, without appendages at base. Petals unequal, posterior ones straight and small, anterior one extended into a lip, with a short spur at base. Stamens connivent around gynoecium; filaments free, short; anthers 2-celled, with a distinct membranous connective appendage, lower two with a patent gland at base. Ovary: ovules numerous, on 3 parietal placentas; style simple, geniculate at base, conspicuously clavate, with an anterior opening stigmatic cavity. Fruit a 3-valved capsule, subglobose, valves leathery. Seeds numerous, ellipsoid, with longitudinal ribs.

About 150 species: chiefly in tropical and subtropical regions of the world; one species in China.