Perennial. Stems weak, ascending, 4-angled, glabrous, (8)-10-20-(50) cm long. Lvs green, sessile except on overwintering vegetative shoots, connate in pairs, lanceolate to oblanceolate to narrow-oblong, becoming linear-lanceolate above, tapering gradually to acute apex and glabrous or ciliate base, (5)-8-12-(25) × 2-5-(8) mm; margins usually closely undulate when dry; marginal vein ± distinct. Infl. axillary, cymose, lax, (1)-3-10-flowered. Bracts narrow-lanceolate, not keeled, scarious with green midrib, glabrous, 1.5-3 mm long. Pedicels slender, erecto-patent to patent, glabrous, 8-18 mm long. Sepals narrow-triangular, acute, 3-veined, (2)-2.5-3 mm long; margins scarious, glabrous. Petals < sepals. Stamens 10. Capsule narrow-ovoid, = sepals. Seeds red-brown, c. 0.5 mm long, with very short tubercles.