<Tr> <Td_colspan="2"> <P> Cynanchum rossicum (Kleopow) Borhidi </P> </Td> </Tr> <P> Cynanchum rossicum (Kleopow) Borhidi </P> <P> Vincetoxicum rossicum is a flowering plant of the milkweed family . It is a perennial herb native to southern Europe and is a highly invasive plant growing in all of the Eastern United States, in the mid west, and southern Ontario and Quebec in Canada . It has several common names including swallowwort, pale swallowwort, and dog - strangling vine . There has historically been much confusion about the genus it belongs to, with authors placing it within Vincetoxicum and others within Cynanchum, but recent molecular and chemical analyses have shown it to belong in the genus Vincetoxicum . </P> <P> The leaves of the pale swallowwort are larger when they are closer to the stem and decrease in size as they move away from the stem . They are in the shape of an ellipse or an oval and contain smooth margins and major veins underneath . The glossy, dark green leaves grow opposite on the stem and are ovate to elliptical . The flowers appear near the top of the plant and grow on stalks that come from the leaf axils . </P>

Where did the dog strangling vine come from