How to identify pale and black swallow-wort:
Pale Swallow-wort (Cynanchum rossicum syn. Vincetoxicum rossicum)
Leaves: Leaves are opposite in arrangement, oval to wedge-shaped with pointed tips. Generally, the leaves are 2.5″ to 4.5″ long and 2″ to 2.75″ wide, glossy and medium green in color. In summer, the leaves begin to display a warm, yellow color.
Flowers: The star-shaped flowers are small and fleshy, with 5 pink to reddish colored petals. They are borne in loose clusters and are visible in late May through mid-July.
Fruit/Seeds: The fruit is a smooth, slender, pointed pod that looks much like a milkweed pod. The pods are light green in color and are frequently borne in pairs. They are abundant during July and August. Like milkweed, the pods open in late summer, disseminating large numbers of downy seeds. They can produce 2,000 seeds per square yard.
Black Swallow-wort (Cynanchum louiseae syn. Vincetoxicum nigrum)
Characteristics are similar to pale swallow-wort, but black swallow-wort leaves are dark green, shiny, and larger in size ranging from 3-4″ long and 2-3″ wide. Flowers are dark purple/blackish in color, and bloom in June to July.