Stout herb to 1 m high; branches tomentose with erect glandular hairs. Leaves broad-ovate, mostly 6–20 cm long, 3–12 cm wide, virtually entire, apex acute, base cuneate, often asymmetric, lower surface sparsely to densely tomentose, upper surface less so; petiole to c. 10 cm long. Flowers erect on short indistinct pedicels; calyx 3–6-lobed, 5–11 cm long, lobes 13–20 mm long, sometimes not completely separating; corolla 12–19 cm long, white with green veins, limb undulate, apparently 10-lobed, alternate lobes triangular or ending in a slender point 5–10 mm long; stamens not exserted, anthers 8–10 mm long; style 10–14 cm long, stigma well below anthers. Capsule subglobose, 3–5 cm long, deflexed, spiny, opening irregularly; spines numerous, slender, sharp, c. equal in length, to c. 10 mm long; persistent calyx-base to 20 mm long; seeds 4–5 mm long, brown. Flowers mainly summer.