Black swallow-wort

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Quick facts

Black swallow-wort is an invasive species on the Prohibited Eradicate List. Plant 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.
The Minnesota Department of Agriculture monitors this invasive species. Please report any black swallow-wort you spot at Arrest the Pest.

tree covered in black swallow-wort in woods

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 filament at the tip.

Roots

Fleshy with a thickly budded rhizomatous crown just below the soil surface.

Angela Gupta, Extension educator; Amy Rager, Extension educator; Megan M. Weber, Extension educator

Reviewed in 2019