Slender, suberect or ±twining or scrambling; peduncles 1-3 cm; cor ochroleucous to maroon or pinkish, its lobes lanceolate, 2.5-4.5 mm, half as wide, glabrous, scarcely fleshy; corona deeply 5-lobed; 2n=22; otherwise much like no. 1 [Vincetoxicum nigrum (L.) Moench], for which it is often mistaken. Native of Europe, occasionally intr. into thickets and waste places in our range. June- Sept. (? V. medium and Cynanchum medium, the former name illegitimate)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.