Shrubs herbs or twiners. Leaves alternate, entire, sometimes reduced to minute scales; stipules absent. Flowers irregular, bisexual. Sepals 5, free, much imbricate; the two inner wings usually larger and petal-like. Lower 3 petals connate forming a concave keel which encloses the stamens and ovary; two upper petals free. Stamens 8; filaments connate to above the middle in a sheath open on the upper side, epipetalous; anthers opening by apical pores. Ovary superior, 2-locular; ovules pendulous. Fruit a compressed capsule. 18 gen., temp. to trop.