Description from Flora of China
Shrubs or small trees, usually unarmed. Leaves bipinnate, eglandular; stipules often persistent, or sometimes spinescent, rarely absent; pinnae 1 to several pairs; leaflets opposite, small and numerous, or larger and from few pairs to only 1. Heads globose and axillary, or racemes terminal. Flowers (5 or)6-merous, polygamous. Calyx campanulate, toothed. Petals united to middle; middle flowers sometimes heteromorphic with an elongated tubular corolla. Stamens numerous (to 100), red or white, ± united into a tube and long exserted, showy; anthers mostly glandular hairy. Ovary sessile, ovules numerous; style filiform. Legume slightly falcate, strap-shaped, flat, rigidly leathery, often narrowed to base, margin thickened, 2-valved, valves elastically opening from apex to base, continuous inside. Seeds obovoid or orbicular, compressed, testa hard, with pleurogram, without aril.
Calliandra riparia Pittier, native to South America, is not treated here because it is only cultivated in China and not commonly so.
About 200 species: mainly in tropical and subtropical regions of the Americas, a few in India, Madagascar, and Myanmar; two species (one introduced) in China.