Description from Flora of China
Subshrubs [or trees, shrubs, or perennial herbs]. Leaves bipinnate; stipules persistent, setaceous; pinnae [1-]2-6[-15] pairs; leaflets small; petiolar gland often between lower pair. Heads solitary, axillary, ovoid-globose. Flowers all bisexual, or lower male or neuter and sometimes without petals but with short staminodes. Calyx campanulate, shortly dentate. Petals free or nearly so. Stamens [5 or]10, free, exserted; anthers eglandular at apex. Ovary subsessile; ovules numerous; style subulate or thickened distally; stigma terminal. Legume straight or falcate, linear, plano-compressed to terete, 2-valved, continuous within or subseptate between seeds. Seeds oriented lengthwise or oblique, ovoid to ellipsoidal, compressed.
About 24 species: mainly in tropical and subtropical regions of the Americas; one species (introduced) in China.