Perennial or annual herbs, sometimes obscurely gland-dotted, rooting at nodes. Leaves opposite, sometimes clustered by suppression of internodes, lamina broader or thicker than petiole, margins entire. Flowers solitary in leaf-axils; bracteoles absent. Calyx tubular, smooth, teeth 3 or 4, short, unequal; corolla 2-lipped, usually 5-lobed, shortly exceeding calyx, tube symmetrical at base, neither swollen nor spurred, upper lip usually 2-lobed, lower usually 3-lobed, without a palate; stamens 4 in pairs of unequal length, or 2, usually included in corolla-tube, anthers of pair(s) joined, 1-locular, staminodes absent; stigma with a small vestigial flap, and a broad irritable flap, covering the corolla mouth, receptive above, when triggered appressed to the upper corolla-lip. Capsule thin-walled, loculicidal from the apex into 2 valves; seeds many, not winged, reticulate.
5 species, all in Australia (3 endemic); also in New Zealand, India and eastern Africa.
The relative conspicuousness of the midvein on the petiole and blade has been determined from spirit-preserved material.