Two species of dog-strangling vine, also known as swallow-wort, have been introduced from Europe and have become highly invasive weeds in eastern North America. Pale swallow-wort is native to the grasslands of European Russia and Ukraine, while black swallow-wort is found in Spain, southern France and northern Italy. Although neither species is very abundant in its homeland, in North America, both species form dense mats of intertwined stems that choke out other vegetation.
Pale swallow-wort is the more common of the two species in Ontario and upstate New York. It has pale maroon, star-shaped flowers that mature into long narrow seed pods. Black swallow-wort is more common in the New England states. Although the leaves are hard to distinguish from those of pale swallow-wort, the flowers are much darker and the seed pods shorter and wider.
Pale swallow-wort is the more common of the two species in Ontario and upstate New York. It has pale maroon, star-shaped flowers that mature into long narrow seed pods. Black swallow-wort is more common in the New England states. Although the leaves are hard to distinguish from those of pale swallow-wort, the flowers are much darker and the seed pods shorter and wider.
Dog-strangling vine
Pale swallow-wort Vincetoxicum rossicum Cynanchum rossicum |
Black dog-strangling vine
Black swallow-wort Vincetoxicum nigrum Cynanchum louiseae |