Cynanchum nigrum, Pers. (Vincetoxicum nigrum, Moench)
Time of bloom: June to September.
Seed-time: August to October.
Range: Massachusetts to Michigan, Pennsylvania, and Ohio.
Habitat: Old fields, fence rows, thickets, and waste places.
Fig. 222. - Black Swallow-wort (Cynanchum nigrum). X 1/4.
This plant, like the preceding one, is often called Climbing Milkweed; the milky-juices are poisonous. It is an immigrant from Europe, first planted in gardens for its beauty; but the silken-winged seeds made an easy escape and now the weed is a frequent nuisance in ground not under cultivation. (Fig. 222.)
Stems twining, slender, three to six feet long, slightly hairy, often brownish red where exposed to the light. Leaves opposite, long-ovate, thin, dark green, smooth, entire, pointed at tip and rounded at base, with prominent, sometimes reddish, veins and short petioles. Flowers in axillary cymose clusters, small, saucer-shaped, the five spreading lobes somewhat twisted, hairy within, deep purple; peduncles shorter than the leaves. Follicles about two inches long, pointed at both ends, smooth. Seeds flat, brown, tipped with silken floss.
Means of control the same as for the preceding species. It is more pernicious, and requires persistent treatment.