Ontario Wildflowers website

Black Swallowwort
Cynanchum louiseae
(formerly Cynanchum nigrum)

Other common names: Black Dog Strangling Vine, Dog Strangling Vine

Other scientific names: Cynanchum nigrum, Asclepias nigra, Vincetoxicum nigrum

Family: Dogbane Family (Apocynaceae), (Milkweed Family (Asclepiadaceae))

Group: Swallowworts

Distinctive features: Opposite leaves on a vine, milkweed-like seed pods and seeds.

Similar species:
  •   Pale Swallowwort (Cynanchum rossicum) - very similar.

  •   White Swallowwort (Cynanchum vincetoxicum) - very similar, has white flowers.


Flowers: Summer;  Green/Brown;  5 parts (petals);  5-petals, dark purple/dark brown, petals fuzzy, 1/4" wide, late spring & summer.

Leaves: Opposite/Whorled, Entire;  Opposite pairs, sometimes in a whorl, egg-shaped.

Height: Vine, 2-6 feet long.

Stem: Vine.

Fruit/Seeds: In a pod closely resembling those of milkweed. but smaller.

Habitat: Fields and Open Areas;  Open areas, forest edges.

Books: Newcomb's Wildflower Guide: 326    Peterson's Field Guide to Wildflowers: 390    ROM Field Guide to Wildflowers of Ontario: 139   

Native/Non-native: Non-native

Status: Common.

Notes: This is a highly invasive alien plant, that will aggressively take over an area once it gets a chance. Pull it up before it gets a foothold.

Origin and Meaning of Names:
 Scientific Name: nigrum: black


See Also:
  •   Swallow-wort: Monarch Menace, from The Monday Garden, by Sue Sweeney


Photographs: 5 photographs available, of which 3 are featured on this page. SCROLL DOWN FOR PHOTOGRAPHS.

Range Map is at the bottom of the page

Black Swallowwort (Cynanchum louiseae)

A flower, showing the fuzzy petals.

Black Swallowwort (Cynanchum louiseae)

Black Swallowwort (Cynanchum louiseae)

Closeup of the side of a flower.


Range map for Black Swallowwort (Cynanchum louiseae)

PLEASE NOTE: A coloured Province or State means this species occurs somewhere in that Province/State.
The entire Province/State is coloured, regardless of where in that Province/State it occurs.

(Range map provided courtesy of the USDA website and is displayed here in accordance with their Policies)