Description from Flora of China
Herbs annual, erect. Stems and branches green. Roots aromatic. Leaves simple, alternate, petiolate or sessile; leaf blade green, elliptic, ovate, or ovate-lanceolate, membranous or papery, margin entire. Inflorescence spicate, terminal, bracts with a scarious margin, bracteoles absent. Flowers very small, zygomorphic. Sepals 5, persistent, nearly equal; inner 2 often slightly larger. Petals 3, usually pink-purple; keel cucullate, or arched, longer than lateral petals, without appendages. Stamens 4; filaments united, forming trough-shaped sheath, adnate with petals, open on upper side; anthers connate, dehiscent by an apical pore. Disk absent. Ovary compressed, 2-loculed; ovule 1 per locule, anatropous; style curved, thickened toward apex; stigma capitate. Capsule reniform, broadly orbicular, or obcordate, compressed, margin denticulate, dehiscent by abaxial suture, with 2 seeds dehiscent. Seeds black, shiny, ovoid, glabrous, with endosperm, not strophiolate.
About five species: tropical Asia, tropical Australia; two species in China.