Erect, annual herb, 6-45 (-70) cm tall. Stem unbranched, slender, scabridulous-papillose, circular or rarely obtusely quadrangular, internodes up to 10 cm long. Leaves opposite, linear or narrowly lanceolate, 1-5 cm x 1-8 mm, acute, margin recurved, upper surface scabridulous, rarely glabrescent; stipules 1-3 mm long, ending in 2-6 filiform, 1.5-3 mm long appendages. Inflorescence laxly branched, of 1-few flowered cyme. Flowers pedicellate, pedicels 0.5-7 mm, enlarged in fruit Calyx-tube densely papillose, ellipsoid 1-1.5 mm long, lobes subulate, c. 2-4.5 mm long, margin ± scabrid, elongated in fruit. Corolla scarlet, pink or purple, glabrous or scabridulous above; tube 3-6 mm long, dilated above, dilated portion c. 2.5 mm, lobes 1.5-3 x 0.8-1.5 mm, oblong-elliptic, obtuse; anthers 0.8-1.0 mm. Style 1-1.5 mm long; stigma c. 1 mm long. Capsule oblong, subglobose or elliptic 3-6 x 2.5-4.0 mm, minutely scabrid, with a slightly raised, dark brown c. 0.3 mm long beak.