Trees, shrubs or usually herbs, usually aromatic, mostly with quadrangular branches. Leaves opposite or rarely whorled; stipules absent. Inflorescence cymose, with flowers often axillary or in the axils of leaf-like bracts, often in whorl-like clusters or reduced to single flowers. Flowers bisexual, usually with at least the corolla zygomorphic and usually 2-lipped; sepals 5, c. connate, persistent; petals 5, connate into a tube; stamens 4, adnate to corolla-tube, often with only 2 fertile, anthers (rarely 1- or)2-locular; ovary superior, 2-carpellate, 4-loculate, usually 4-lobed; style c. gynobasic. Fruit a schizocarp with each mericarp 1-seeded.
About 236 genera and 7200 species, cosmopolitan; c. 70 genera and 550 species in Australia.