A genus of about 25 species of the Neotropics, with several introduced into the Old World.
Habit
Shrubs or perennial herbs.
Leaves
Leaves bipinnately compound, leaflets small, opposite, often with a petiolar gland, stipules small, subulate, persistent.
Flowers
Flowers mimosaceous, perfect, sometimes those in lower part of inflorescence staminate or neutral, these without petals but with staminodes, each one minute, in axillary, solitary, stalked heads or short spikes, bracteoles absent; calyx campanulate, shortly 5 lobed; petals distinct or slightly coherent at base; stamens 5-10; filaments distinct, exserted; ovules numerous.
Fruit
Pods linear, straight or curved, flattened, dehiscent, valves thickened or membranous.
Seeds
Seeds more than 15, longitudinally or obliquely arranged, ovoid, compressed, without a pleurogram.