This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Stem downy, slender. Leaves ovate, acuminate at the apex, deeply cordate at the base, downy, 2'-4 long, 1'-2 1/2' wide, the sinus narrow, or the lobes sometimes overlapping; petioles slender, pubescent, i'-2' long; peduncles usually about equalling the petioles, sometimes longer; umbels few-several-flowered; corolla brown-purple to greenish yellow, ovoid in the bud, its segments oblong, very obtuse, 3 "-4" long, minutely puberulent without, about 4 times as long as the densely pubescent calyx; crown cup-shaped, fleshy, about as high as the anthers, the margin 10-crenate; follicles lanceolate, 2'-5' long, muricate, puberulent; seeds entire.
Cynanchum hirtum L. Sp. Pl. 212. 1753? Cynanchum obliquum Jacq. Coll. 1: 148. 1786. G. obliquus R. Br.; R. & S. Syst. 6: 64. 1820. V. obliquum Britton, Mem. Torr. Club 5: 266. 1894.
Stem puberulent or hirsute, slender. Leaves pubescent, broadly ovate, short-acuminate at the apex, deeply cordate at the base with an open or closed sinus, 2's' long, 1 1/2'-6' wide; petioles rather stout, pubescent, 1'-4' long; umbels slen-der-peduncled, few-several-flowered; pedicels very slender, 1'-2' long; corolla narrowly conic in the bud, red-purple within, greenish and minutely pubescent without, its segments elongated-linear, obtuse, 6-7 times as long as the hirsute calyx; crown cup-shaped, as high as the anthers, fleshy, its margin 10-crenulate, the intermediate crenu-lations sometimes 2-dentate; follicles ovoid-lanceolate, 2-3' long, muricate.
In thickets, Pennsylvania to Ohio, Missouri, Virginia and Kentucky. July-Aug.
Cynanchum carolinense Jacq. Coll. 2: 228. 1788. G. carolinensis R. Br.; R. & S. Syst. 6: 62. 1820. V, carolinense Britton, Mem. Torr. Club 5: 265. 1894.
Stem hirsute. Leaves broadly ovate, acute or shoTt-acuminate at the apex, deeply cordate at the base with a narrow or closed sinus, 3'-7' long, 2'-5 1/2 wide, pubescent, at least beneath; petioles hirsute, 1 1/2'- 4' long; peduncles 2'- 4' long; pedicels very slender, 1' long or more; corolla brown-purple, oblong-conic in the bud, puberulent without, its segments linear-oblong or linear-lanceolate, obtusish, 5'-6" long, 5-6 times longer than the hirsute calyx; crown cup-shaped, scarcely fleshy, 5-lobed, with a subulate longer 2-cleft erect tooth in each sinus; follicles muricate.
In thickets, Virginia to Missouri, south to South Carolina and Louisiana. May-July.