Shrub to c. 2 m tall. Stems 4-angled, markedly square on vigorous vegetative shoots. Lvs glabrous, those on flowering shoots with petioles to 3 cm long. Lamina of flowering shoots 2.5-6.5 × 1.5-3 cm, ovate or lanceolate-ovate, evenly crenulate-serrulate; base broad-cuneate to subcordate; apex obtuse or subacute. Infl. of many pendent fls at right angles to pedicels. Bracts to c. 1 cm long. Peduncles mostly 1-2.5 cm long, shortly glandular-hairy, dark reddish. Pedicels similar to but < peduncles. Calyx 4-6 mm long, lanceolate to ovate, glabrous, purplish. Corolla 3-3.5 cm long, deep red outside, yellow inside; tube curved; limb oblique, the lower lobes slightly > upper. Stamens shortly exserted. Filaments red. Capsules 10-13 mm long, shining black, furrowed. Seeds 1-1.2 mm long, oblong to ovoid, sometimes angled.