5–30 cm (2–12 in.).
Corolla almost regular (actinomorphic), white and usually bluish–purpleish, 3–6 mm (0.12–0.24 in.) wide, fused, 4-lobed, wheel-shaped, short-funnelled. Calyx 4-lobed, lobes ovate, quite blunt, not overlapping, hairy at least on outside. Stamens 2. Gynoecium fused, single-styled. Flowers solitary in leaf axils. Flower-stalk curves downwards in fruiting stage.
Opposite, short-stalked. Blade widely ovate, longer than broad, blunt-based, shallowly serrated with rounded teeth (crenate).