Vincetoxicum nigrum (Black Swallow-wort)

Plant Info
Also known as: Black Dog-strangling Vine
Family:Apocynaceae (Dogbane)
Life cycle:perennial
  • Invasive - ERADICATE!
  • Prohibited or Restricted species
Habitat:part shade, sun; garden escapee; disturbed soil, waste areas, roadsides, woods, thickets
Bloom season:June - August
Plant height:2 to 6 feet
Wetland Indicator Status:none
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

Pick an image for a larger view. See the glossary for icon descriptions.

Detailed Information

Flower: Flower shape: 5-petals Cluster type: panicle

[photo of flowers] Loose, branching clusters of up to 10 stalked, star-shaped flowers arising from leaf axils. Flowers are about ¼ inch across, dark purple with 5 fleshy petals that are variously covered in minute white hairs on the upper surface. The pale yellow crown in the center is surrounded by a dark purple collar.

Leaves and stems: Leaf attachment: opposite Leaf type: simple

[photo of leaves] Leaves are opposite, 2 to 5 inches long, ½ to 3 inches wide, narrowly to broadly egg-shaped, tapering to a sharply pointed tip, rounded to somewhat heart-shaped at the base, toothless, hairless, shiny, dark green, on short stalks.

[photo of minutely hairy, twining stem] Stems are multiple from the base, unbranched, minutely hairy, lack tendrils, erect when young, later twining around itself and other vegetation for support, creating dense thickets.

Fruit: Fruit type: capsule/pod

[photo of fruit] Fruit is a slender, spindle-shaped pod about 2 inches long. Inside are numerous brown seeds each with a tuft of white hairs to carry it off in the wind.


Related to milkweeds and dogbanes and known as Cynanchum louiseae or Vincetoxicum nigrum, Black Swallow-wort was first introduced in New England or eastern Canada by European settlers in the 1800s. A far more serious pest plant to our east, Black Swallow-wort is on the “eradicate” noxious weed list for Minnesota. Only 2 known populations exist in Minnesota at this time and, according to the MN Dept. of Agriculture, both are actively managed. Perhaps we actually will eradicate it, though the population on the University of MN St Paul campus has been around for over 15 years and, as far as we know, still persists. The root crown is a dense clump of thick rhizomes that allow it to spread vegetatively, and after cutting it resprouts vigorously from buds on the underground crown. Digging out the root crown can be an effective control method, as are certain herbicides. Besides its alleopathic properties that inhibit the growth of native plants, Black Swallow-wort has another claim to fame: as a “fatal” host plant for Monarch butterflies. Monarch larvae that feed on Swallow-worts have a higher mortality rate than those feeding on native milkweeds. Bad plant!

Please visit our sponsors

  • Must have book: Pollinators of Native Plants

Where to buy native seed and plants ↓

Map of native plant purveyors in the upper midwest

  • Itasca Ladyslipper Farm - Native orchids, container grown
  • Prairie Restorations - Bringing people together with the land
  • Shop for native seeds and plants at!
  • Shooting Star Native Seeds - Native Prairie Grass and Wildflower Seeds
  • Morning Sky Greenery - Native Prairie Plants

More photos

Photos courtesy Peter M. Dziuk taken at the University of Minnesota St. Paul campus.


Have you seen this plant in Minnesota, or have any other comments about it?

Post a comment

Note: All comments are moderated before posting to keep the riff-raff out. An email address is required, but will not be posted—it will only be used for information exchange between the 2 of us (if needed) and will never be given to a 3rd party without your express permission.

For info on subjects other than plant identification (gardening, invasive species control, edible plants, etc.), please check the links and invasive species pages for additional resources.


Note: Comments or information about plants outside of Minnesota and neighboring states may not be posted because Id like to keep the focus of this web site centered on Minnesota. Thanks for your understanding.