27. Cynanchum Linnaeus, Sp. Pl. 1: 212. 1753; Gen. Pl. ed. 5, 101. 1754.
Strangle-vine, swallow-wort, milkweed vine [Greek kyon, dog, and ancho, strangle, alluding to toxicity of some species]
Mark Fishbein
Ampelamus Rafinesque; Mellichampia A. Gray; Rouliniella Vail
Vines [erect herbs, subshrubs], herbaceous or somewhat woody, but not corky, at base [succulent]; latex white or clear. Stems twining [not twining], unarmed, puberulent in single line or glabrate [variously pubescent or glabrous]. Leaves persistent [reduced to inconspicuous scales], opposite, petiolate [sessile]; stipular colleters interpetiolar; laminar colleters present [absent]. Inflorescences extra-axillary, racemiform, corymbiform, or paniculiform [umbelliform], sessile or pedunculate. Flowers: calycine colleters apparently absent [present?]; corolla white, cream, or green [brown, purple, red, pink], campanulate [rotate], aestivation imbricate; corolline corona absent; androecium and gynoecium united into a gynostegium adnate to corolla tube; gynostegial corona 1-[2-]whorled; anthers adnate to style, locules 2; pollen in each theca massed into a rigid, vertically oriented pollinium, pollinia lacrimiform, joined from adjacent anthers by translators to common corpulsculum and together forming a pollinarium. Fruits follicles, usually solitary, variously oriented, green to brown, terete or subterete, smooth, glabrous. Seeds winged, not beaked, ovate, flattened, comose, not arillate. x = 11.
Species ca. 300 (3 in the flora): United States, Mexico, West Indies, Central America, South America, Europe, Asia, Africa, Indian Ocean Islands (Madagascar), Australia.
The influential revision of North American milkweed genera by R. E. Woodson Jr. (1941) adopted a very broad (and evidently polyphyletic) circumscription of Cynanchum, reducing genera recognized here to synonymy (Metastelma, Orthosia, Pattalias). Similarly, regional floras for Canada and the United States have included the introduced species here treated in Vincetoxicum under Cynanchum. The polyphyly of this broad concept of Cynanchum has been convincingly demonstrated (for example, by S. Liede and A. Täuber 2002). Another potential source of confusion is that the species of Funastrum have previously been included in the Old World genus Sarcostemma R. Brown. Although Sarcostemma has been synonymized with Cynanchum following the phylogenetic results of Liede and Täuber, the species of Funastrum are distantly related to those of Cynanchum.
SELECTED REFERENCES Liede, S. and A. Täuber. 2002. Circumscription of the genus Cynanchum (Apocynaceae–Asclepiadoideae). Syst. Bot. 27: 789–800. Sundell, E. 1981. The New World species of Cynanchum subgenus Mellichampia (Asclepiadaceae). Evol. Monogr. 5: 1–63.
