Lianas , twining, to 20 m, woody. Young stem ribbed, glabrous. Leaves: petiole 4-6 cm. Leaf blade reniform, 7-34 × 10-35 cm, base cordate, sinus depth 1-4.5 cm, apex obtuse to acute or acuminate; surfaces abaxially glabrous to slightly puberulent; venation palmate-pinnate. Inflorescences on new growth, axillary, solitary flowers; peduncle bracteolate, 3-7 cm; bracteoles reniform, to 15 mm. Flowers: calyx yellow-brown marked with red-brown, strongly curved; utricle pendent, globose to cylindric, 0.5-1.5 × 0.8-1 cm; syrinx absent; tube curved or bent and angled upward, cylindric, 1-3 × 0.3-0.5 cm; annulus smooth; limb yellow to brown, 3-lobed, lobes 1.5-2 × 1.5-2 cm, glabrous; gynostemium 3-lobed, globose to crown-shaped, 4 mm; anthers 6; ovary 3-locular, 3-7 cm. Capsule ovoid to cylindric, 6-8 × 4-10 cm, dehiscence basipetal; valves 6; septa entire, not attached to valves. Seeds * flat, triangular, 1 × 1 cm. 2 n = 28. Flowering late spring-summer. Forests, often on dissected uplands and rugged, rocky slopes; Cumberland and Blue Ridge mountains; 50-1300 m; Ont.; Ga., Ky., Md., N.C., Pa., S.C., Tenn., Va., W.Va. Aristolochia macrophylla has possibly escaped from cultivation in Connecticut, Maryland, Massachusetts, New Jersey, New York, and Vermont; these are not documented.
High-climbing woody twiner; lvs broadly round-cordate, 1-4 dm long and wide, glabrous, or minutely hairy beneath; peduncles solitary or few together in the axils, glabrous, very slender, bearing near the middle a cordate-clasping, foliaceous bract 1-2 cm wide; perianth glabrous, strongly bent, 4 cm, much dilated at base, gradually narrowed to the throat, the limb dark madder-purple, 2.5 cm wide, subequally 3-lobed; fr cylindric, 5-8 cm. Rich mt. woods; Appalachian region from s. Pa. to n. Ga.; cult. and escaped northward. June. (A. durior, probably misapplied)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.