Procumbent or ascending annual or short-lived perennial herb, with stems up to 50 cm. Leaves opposite, more or less narrowly ovate or elliptic, 1.2 - 6 cm long, hairless or finely velvety; margin entire or with blunt triangular teeth. Flowers in 1-12-flowered clusters, together forming spike-like or branched inflorescences up to 30 cm long. Corolla mauve, blue, purple or rarely white, almost actinomorphic, 5-lobed. Capsule 4-7 mm long, finely velvety, with a few glands near the apex.