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European Swallow-worts Cynanchum rossicum/Cynanchum louiseae (Vincetoxicum medium/Vincetoxicum nigrum)


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Black (left) and Pale (right) Swallow-worts
© Leslie J. Mehrhoff, University of Connecticut/

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Alternate name: Pale Swallow-wort, Black Swallow-wort

Family: Asclepiadaceae, Milkweed view all from this family

Description Introduced. Upright or twining vines that bear milkweed-like seed pods that split open to reveal cottony fibers, which help disperse the seeds.
Flowers: small, star-shaped, with triangular petals; pinkish or pinkish-tan to dark purple or purplish-brown; in small clusters.
Leaves: to 5" (12.5 cm) long, half as wide; pointed.
Height: varies; can grow upright to about 5' (1.5 cm) tall or twine up other plants or surfaces.

Warning Toxic white sap found inside stems and leaves of Cynanchum species makes these plants poisonous if ingested.

Habitat Fields, roadsides, disturbed areas, woods, edges, and some wetlands.

Range Europe native; naturalized in Ontario, the northeastern United States, west to Nebraska and Kansas, and in California.

Discussion European or Pale Swallow-wort (C. rossicum) and the similar Black Swallow-wort (C. louiseae) are considered invasive weeds in parts of the United States where they have spread into natural habitats. Their wind-blown seeds help them spread. They can quickly take over acres of cleared or otherwise open land, crowding out native species.