Hairy, perennial herb; stems erect, ± quadrangular, 1-2 m tall, pink towards base. Lvs sessile, 20-95 × 5-27 mm (smaller just below infl.), lanceolate, oblong-lanceolate or narrow-elliptic, with short hairs beneath, especially on veins, sometimes becoming glabrous above, entire, ciliolate; base usually rounded to cordate, sometimes amplexicaul; apex usually acute, sometimes subacuminate. Infl. terminal, branched, main axis to nearly 25 cm long, densely hairy. Fls usually dense except on lower branches, usually in whorls of 3-7, sometimes 1-2 in axils of bracts, or to 15 per whorl, tristylous. Pedicels c. 0.5 mm long; bracteoles much > pedicels. Calyx 6-8 mm long, broad-cylindric, often purplish, with prominent ribs, hairy; calyx lobes ± triangular; epicalyx segments 1.5-2.5 mm long, subulate, much > lobes, densely hairy. Petals 6, 9-15 mm long, rose or rosy purple, crumpled; claw short; limb oblong-elliptic or oblong-obovate. Stamens usually 12, usually 6 exserted and 6 included, rarely all exserted. Style to 7 mm long, with stigma at varying levels in different plants. Capsule included, 3-5 mm long, ellipsoid or ovoid-ellipsoid, blackish. Seeds 0.8-1.2 mm long, narrow-ovoid to almost oblong, ± flattened and keeled on one side.