5–20 cm (2–8 in.). Stem limp, base branching, sparsely haired.
Corolla almost regular (actinomorphic), blue, 3–6 mm (0.12–0.24 in.) broad, fused, 4-lobed, wheel-shaped, short-tubed. Calyx 4-lobed, lobes broadly ovate, with tapering tips, bases overlapping even in fruiting stage, glabrous but with hairy margins. Stamens 2. Pistil a fused carpel. Flowers solitary in axils. Flower-stalk curving downwards in fruit.
Opposite, short-stalked. Blade ovate–broadly elliptic, often shorter than broad, shiny, virtually glabrous, deeply serrated.