Erect or decumbent annual herb; stem up to 25 cm long.
Leaves opposite, oblong-ovate, 4-6 cm long, sparsely silvery hairy,particularly on the veins; margin with a pair of large teeth in the lower third and sometimes coarsely toothed towards the apex; petiole very short, 0-2 mm long, not winged but with the base of the leaf somewhat decurrent.
Flowers solitary, axillary, on pedicels 3-6 mm long (up to 9 mm in fruit).
Calyx finely velvety with scattered capitate glands. Corolla white with or without a pale yellow centre; tube cylindric for about 2 mm, opening to the throat for 7-10 mm and 3-5 mm wide at the apex; lobes 3-5 mm long; anthers c. 1.5 mm long, bearded at the base. Capsule depressed globose, 6-10 mm wide with a beak 8-12 mm long, densely velvety.