Herbs , erect, to 1 m. Young stem ribbed, glabrous to puberulent. Leaves: petiole 4-7 cm. Leaf blade deltate to reniform, 4-6 × 5-6.5 cm, base cordate, sinus depth 1-2 cm, apex obtuse to rounded; surfaces abaxially glabrous; venation palmate. Inflorescences on new growth, axillary, fascicles or solitary flowers; peduncle not bracteolate, 1-4 cm. Flowers: calyx yellow-brown, curved; utricle angled upward, ovoid to globose, 0.5 × 0.2-0.3 cm; syrinx absent; tube curved upward, cylindric, 1-3 × 0.2-0.3 cm; annulus absent; limb purple, 1-lobed, lobe funnel-shaped, 1-6 cm, pilose; gynostemium 3-lobed, globose, 1-4 mm; anthers 6; ovary 6-locular, 1-4 cm. Capsule ± globose, 3 × 2-3 cm, dehiscence basipetal; valves 6; septa entire, not attached to valves. Seeds flat, triangular, 1 × 1.2 cm. Flowering summer. Waste places, roadsides, ballast; 0-100 m; introduced; Ont., Que.; Md., Mass., N.Y., Ohio, Pa.; Europe. Aristolochia clematitis is occasionally cultivated, sometimes escapes, and probably does not persist.

Stems ascending or reclining, 5-10 dm; lvs broadly cordate, 5-10 cm long and wide, blunt to subacute, pale beneath, the broadly rounded basal auricles somewhat incurved below the rounded sinuses; fls in small axillary fascicles, the yellow perianth nearly straight, 3 cm, enlarged around the ovary, terminating in an ovate lobe on one side; 2n=14. Native of s. Europe, occasionally escaped from cult. in our range. Summer.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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