Perennial herbs or shrubs; branches quadrangular with simple, rarely branched hairs, sessile glands usually present. Leaves sessile or petiolate, opposite, simple or trifoliolate, margin entire, serrate or lobed. Inflorescence a thyrse, with 1–many pedicellate or sessile flowers in axillary cymes. Calyx 5-lobed, lobes c. equal, acute (in Victoria); corolla 1-sided, 5-lobed, the stamens exserted from the deep division between the 2 most adaxial lobes, white or cream; stamens 4, fertile, usually greatly exserted, anthers with both locules fertile; ovary scarely 4-lobed, style inserted near apex of ovary, stigma 2-fid. Mericarps not or only slightly keeled, with a deep concavity near the point of attachment, glandular and with some apical hairs.
About 300 species, cosmopolitan with the Mediterranean as a centre of diversity; c. 13 species in Australia.