Quick facts
Black swallow-wort is an invasive species on the Prohibited-Eradicate Noxious Weed list. Plants must be destroyed and transportation, propagation, or sale of these plants is prohibited.
- Black swallow-wort grows in sunny and shady areas, such as gardens, roadsides, wooded edges, quarries, pastures and fence rows.
- It grows in a dense, viny mat.
- Leaves are fatal to monarch caterpillars who mistake it for milkweed.
- If you find suspected black swallow-wort in Minnesota, please report it via EDDMapS or Report a Pest. Make sure to include identifying characteristics in photos and record its exact location with either an address or the location’s GPS coordinates. For more information on these species, visit the MDA’s Noxious Weed List webpage.
How to identify black swallow-wort
Black swallow-wort (Cynanchum louiseae) is an herbaceous perennial in the milkweed family.
Stem
- It is a vine with twining stems up to 6 inches long.
Leaves
- Lance-shaped with smooth edges.
- Opposite, dark green, and glossy.
Flowers
- Star-shaped flowers are 1/8 inch, purple with a yellow center, and occur in clusters at leaf axils.
Fruit
- Typical milkweed-like pod, up to 2-1/2 inches long, 3/8 inch diameter, and smooth.
Seeds
- When mature, pods open to release rounded, flattened brown seeds with silky threads at the tip.
Roots
- Fleshy with a thickly budded rhizomatous crown just below the soil surface.
Reviewed in 2019