Black swallow-wort (Cynanchum louiseae) - Early Detection Species

Black swallow-wort is considered a early detection species not present or with a limited distribution in Minnesota.

photo: Asian long-horned beetle


Appearance: Perennial, herbaceous vine in the milkweed family. Vines can grow up to 6 ft long.

Leaves: Opposite, lance-shaped, with smooth edges.

Flowers: Purple flowers with yellow center, five petals with small hairs on the petals, flowers arranged in clusters from the leaf axils. Flowers from late May to mid-July.

Seeds: Seeds are in milkweed seedpods 1.5 - 3 inches long. Seed pods open in late summer and early fall and release wind-borne seeds on silky filaments.


Ecological Threat:

  • Grows aggressively and forms dense patches that can cover other species in forests, grasslands, and savannas.
  • May have negative impacts on monarch butterflies by displacing the native milkweeds upon which monarchs' depend. Additionally, swallow-wort may serve as a fatal host to monarch larvae. When monarch butterflies lay eggs on black swallow-wort, the butterfly larvae are unable to develop on black swallow-wort and die. It is unknown how large of impact this has on monarch populations.
  • Black swallow-wort is a MDA Prohibited Noxious Weed (Eradicate List) in Minnesota meaning that above and below ground parts of the plant must be destroyed. Additionally no transportation, propagation, or sale of black swallow-wort is allowed.

Report black swallow-wort by emailing "Arrest the Pest" or calling 651-201-6684 (metro) or 1-888-545-6684 FREE (toll-free) 


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