Lianas , twining, to 25 m, woody. Young stem ribbed, tomentose. Leaves: petiole 1-5.5 cm. Leaf blade ovate to reniform, 9-20 × 8-15 cm, base cordate, sinus depth 1-2 cm, apex obtuse to acute; surfaces abaxially tomentose; venation palmate-pinnate. Inflorescences on new growth, axillary, solitary flowers; peduncle not bracteolate, 1-7 cm. Flowers: calyx yellow-green, sharply bent; utricle pendent, globose to cylindric, 0.5-1 × 0.5-0.8 cm; syrinx absent; tube bent, cylindric, 1-3 × 0.5 cm; annulus rugulose; limb yellow, 3-lobed, lobes triangular, 2 × 2 cm, glabrous; gynostemium 3-lobed, globose, 3 mm; anthers 6; ovary 6-locular, 1-7 cm. Capsule ellipsoid to cylindric, 6-8 × 4-6 cm, dehiscence basipetal; valves 3; septa entire, not attached to valves. Seeds flat, triangular, 1 × 1 cm. 2 n = 28. Flowering late spring-summer. Alluvial soils along rivers and streams; to 500 m; Ala., Ark., Fla., Ga., Ill., Ind., Kans., Ky., La., Miss., Mo., N.C., Okla., Tenn., Tex. Aristolochia tomentosa has escaped from cultivation in various places, including Virginia; this is not documented.
From Flora of Indiana (1940) by Charles C. Deam
Local in the Lower Wabash Valley from the southwestern corner of Knox County southward. It is rather frequent along the lower course of White River in both Gibson and Knox Counties. South of Coffee Bayou in Gibson County it is rare until Point Township in Posey County is reached where it again is local. It climbs to great heights on bushes and small trees. I have seen the dead trunks of large trees shingled with it to a great height. Ridgway (Proc. Nat. Mus. 17: 421. 1894) records the measurements of a vine found in the Lower Wabash Valley as "83 feet long and 10 inches in circumference." I measured a leaf in Posey County, the blade of which was 10 inches wide and 9 inches long. We have had it planted for years as a porch trellis and it serves this purpose well but it spreads vigorously by root suckers.
High-climbing woody twiner; lvs broadly round-cordate, 1-2 dm long and wide, softly hairy beneath, peduncles axillary, solitary or paired, 2-4 cm, densely tomentose, bractless; perianth bent, 4 cm, densely tomentose, nearly closed at the throat, the limb dark madder-purple, spreading to reflexed, subequally 3-lobed; fr cylindric, 6-8 cm; 2n=28. Wet, alluvial woods; s. Ind. to se. Kans., s. to Ga., nw. Fla., and Tex.; locally intr. in Mass. June.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.