Description from Flora of China
Shrubs scandent. Leaves simple, alternate; nodal glands present, veinlets reticulate. Inflorescences racemose or paniculate, terminal or axillary. Flowers zygomorphic, small, with bracts. Sepals 5, caducous, unequal; outer 3 small; inner 2 petaloid, large. Petals 3, lateral petals and keel connate or free, keel helmet-shaped, with apical appendage. Stamens 8; filaments united in lower part, forming trough-shaped sheath open on upper side and adnate to petals; anthers 2-celled, ovoid, dehiscent by oblique pores. Disk reniform. Ovary 1-loculed; ovule 1, anatropous, pendulous; style falcate, curved; stigma short, lobed or not. Fruit usually a samara, with 1 seed; wing oblong or rhombic-oblong, leathery, veins numerous. Seed subglobose, without endosperm, without strophiole; seed coat membranous.
About 80 species: primarily in tropical America, a small number of species distributed in tropical regions of Africa and Asia; two species (one endemic) in China.