Annual, glabrous herb; stems erect, single but branched above, to c. 2.5 m high, succulent, ribbed, swollen at nodes. Petioles to c. 8 cm long, pink above, narrowly winged, with scattered purplish elongated glands in distal 1/2. Lvs opposite or in whorls of c. 3. Lamina 10-20 × 3-8 cm, lanceolate to ovate, sharply serrate; veins impressed above, raised below; base cuneate or attenuate; apex acuminate. Fls in diffuse cymes in upper lf axils of branches, shining. Bracts and lateral sepals 5-10 mm long, ovate, pink, acuminate. Posterior sepal forming large backwards projecting hood 2.2-3 cm long (excluding spur), pink or rose with dark spots inside; spur 5-7 mm long, rather stout, green. Corolla 2-lipped, white or pale pink; uppermost petal 1.5-2 cm long, subreniform; apex truncate to slightly emarginate; lateral petals very asymmetric, c. 3.5 cm long when stretched out, sharply bent in middle with lower halves forming a circular orifice enclosing the elongated anther mass. Anthers yellow. Capsule 2-3 cm long, usually purplish on exposed side, constricted in upper 1/2, with 5 acute ridges. Seed 3.5-5 mm long, ± broadly ovoid, shining black, with a single ridge down 1 side; base truncate; apex slightly beaked.