Black Swallow-wort (Cynanchum louiseae
Kartesz & Gandhi)
European Swallow-wort (Cynanchum rossicum (Kleo.)
Alternate Latin names: Black =
Cynanchum nigrum (L.) Pers.,
Vincetoxicum nigrum (L.) Moench; European =
Vincetoxicum medium (R. Br.) Decne., V.
rossicum (Kleo.) Barb., Cynanchum rossicum
Kleo., Antitoxicum rossicum (Kleo.) Pobed.
twining, herbaceous, perennial vines; 3'-9' long, spiraling around self
and up other plants
leaves opposite; base never heart-shaped; color dark, glossy green, drying
to bright yellow
fruit resembles smooth, slender Milkweed pods 1 1/2"-3" long; surface is
pods change from green to yellow to brown then split on one side to
release windblown seeds
flowers about 1/8" across; flat, star-shaped, light pink to dark purple
with yellow centers
Swallow-wort flowers have the petals united to form a short tube at the base
of the flower while the outer ends of the petals form a flat, 5-parted star.
Petal color and shape distinguish our 2 species of Swallow-worts: Black
Swallow-wort = dark purple, triangular (with microscopic hairs); European
Swallow-wort = light purple, maroon, or pinkish, longer than broad (and yellow
center does not stand out). The 2 invasive Swallow-worts in North America have a
confusing history of name changes. European Swallow-wort (also called Pale
Swallowwort) sometimes has been lumped with White Swallow-wort (under
V. hirundaria Medik. or
Cynanchum medium R. Br.). However, White
Swallow-wort lacks a twining stem and, although it has escaped from gardens, it
has not been found to be invasive in North America.
Black and European Swallow-worts grow in uplands under a wide variety of
moisture and light conditions. They readily choke out native plants. If
incompletely removed, they sprout from fibrous, spreading root systems (Black)
or directly from the base (European). When Milkweed-seeking Monarch Butterflies
lay eggs on Black Swallowwort, the larvae do not survive after hatching.