Glabrous, bushy annual to perennial, 15-150 cm, with tap root. Stems somewhat woody at base, glabrous, occasionally minutely pubescent at nodes, angled. Branches slender, alternate below, becoming opposite above. Leaves opposite-decussate to whorled, linear-oblanceolate or narrowly elliptic to narrowly obovate, 5-40 x 1-18 mm, conspicuously glandular-punctate, at least larger ones shallowly but distinctly serrate in distal half, cuneate at base into indistinct, short petiole, bases of adjacent leaves connected by a membrane. Flowers (1-) 2-4 per leaf axil, forming many-flowered leafy raceme-like inflorescences. Pedicels filiform, c. 5 mm. Calyx divided nearly to base, lobes oblong, 1.5-2 mm, glandular-punctate. Corolla white or greenish-white, 3-5 mm across, lobes ± reflexed, c. 2-3.5 mm, scarcely exceeding calyx, glabrous outside, with dense tuft (beard) of long silky white hairs surrounding stamens. Stamens 4, equal; filaments c. 1 mm; anthers c. 0.7-1 mm, yellow. Style c. 1.5 mm. Capsule subglobose, 2-3.5 x 1.5-3 mm, yellowish-brown, glabrous. Seeds c. 0.5 x 0.15 mm, brown, prismatic, rather irregular in shape, coarsey reticulate.