- Dog-strangle vine
- Cynanchum nigrum, Vincetoxicum nigrum
- An herbaceous, perennial vine growing up to 6.5 feet long. Stems are unbranched but can twine around each other to form thick spirals.
- ovate or ovate-lanceolate
- 2-5 inches long, 0.5-2.5 inches wide
- dark green
- glabrous, shiny
- short petioles
- Dark purple to almost black five-petaled flowers in clusters of six to ten. The corolla is five-lobed, with triangle shaped, fleshy petals. Petals are slightly toothed, with short, straight, white hairs on the upper surface, joined together by a connective membrane. Blooms from June to September.
- resemble narrow milkweed pods
- green maturing to brown
- seeds flat, brown, ovoid, membranous wing on margin
- tuft of white hairs at one end
- woodlands, fields, roadsides, floodplains, uplands
- seeds dispersed primarily by wind, sometimes by water
- also resprouts from cut stems
Key ID Features:
- unbranched vine
- shiny dark green leaves
- clusters of dark purple flowers
- white hairs
- milkweed-like pods with hairs
- Pale swallow-wort (Cynanchum rossicum) has pale yellow-purple to reddish corolla lobes and smooth, hairless corolla lobes that are twice as long as wide. Black swallow-wort (Cynanchum louiseae) has dark purple, deltoid shaped corolla lobes with short white hairs.
- Rapid growth and wind dispersed seeds allow Black Swallow-wort to outgrow and crowd native vegetation.
- This species is a relatively recent arrival on Nantucket. Vines are often found wrapped around other invasive species. Spreading from Sconset.
Growth Form: Vine
Level of Invasiveness for Nantucket: Invasive
Level of Invasiveness for Massachusetts: Invasive
Massachusetts Cultivation Restrictions: importation ban, propagation ban