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..
Twining or trailing perennial vines, with opposite usually cordate leaves, and rather large purple, brown, white or greenish flowers in axillary cyme-like Umbels or fascicles. Calyx 5-parted or deeply 5-cleft, mostly 5-glandular within. Corolla rotate, very deeply 5-parted, the tube very short, the segments convolute in the bud. Corona (crown) annular or cup-shaped, entire, lobed or divided, adnate to the corolla. Stamens inserted on the base of the corolla, the filaments connate into a tube; anthers not appendaged, merely tipped, borne along or just under the margin of the flat-topped stigma, the sacs more or less transversely dehiscent. Pollen-masses solitary in each sac, horizontal or nearly so. Follicles thick, acuminate, smooth, angled or tuberculate. Seeds comose. [Greek, subduing poison.]
About 75 species, natives of America. Besides the following, some 10 others occur in the southern and southwestern United States. Type species: Vincetoxicum gonocarpos Walt.
Crown annular, 10-crenate; follicles angled, not warty. Corolla about twice as long as the calyx.
1. V. suberosum.
Corolla 3-4 times as long as the calyx.
2. V. gonocarpos.
Corolla-segments oblong, 3"-4" long; crown crenate.
3. V. hirsutum.
Corolla-segments linear or linear-oblong, 5" - 7" long. Crown merely crenate.
4. V. obliquum.
Crown toothed or lobed.
Crown 5-lobed, with a subulate 2-cleft tooth in each sinus.
5. V. carolinense.
Crown 10-toothed, the alternate teeth thinner and longer.
6. V. Shortii.
Flowers white; crown deeply cleft.
7. V. Baldwinianum.
Cynanchum suberosum L. Sp. Pl. 212. 1753.
Stem pubescent or glabrous, slender, twining. Leaves thin, 2'-5' long, 1'- 3' wide, ovate or ovate-oval, acute or abruptly acuminate at the apex, cordate at the base; petioles 1/2'-2 long; umbels commonly few-flowered; peduncles 1/4'-1' long; pedicels 1/2'-1' long, fleshy, nearly glabrous; corolla brown-purple, broadly conic in the twisted bud, its segments lanceolate or ovate-lanceolate, acute, pubescent or granulose within, 3'-4" long, about twice as long as the calyx; crown an annular fleshy undulately 10-crenate disk; follicles glabrous, 3-5-angled, when young fleshy, when mature dry and spongy, 4'-6' long, 1' in diameter or more.
In thickets, Virginia to Florida, mainly near the coast.
Glabrous or pubescent, stems slender, climbing high. Leaves broadly ovate, thin, 3'-8' long, 2'-6' wide, acuminate at the apex, deeply cordate at the base, the sinus narrow or the rounded auricles overlapping; petioles 1'- 4' long; umbels few-flowered; peduncles 1'-3' long; pedicels rather stout, glabrous or nearly so; corolla conic in the bud, not twisted, its segments lanceolate, glabrous, 4"-5" long, 3-4 times as long as the calyx; crown a low obtusely undulate disk; follicles glabrous, similar to those of the preceding species but usually shorter.
Along rivers and in moist thickets, Virginia to South Carolina, Georgia, Indiana Missouri and Texas.