Black Swallow-wort
Cynanchum louiseaeAsclepiadaceae
Whole Plant
Flower
Fruit
Leaf
Whole PlantFlowerFruitLeaf
Leaf
Habitat
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Photos (c) Cheryl Comeau Beaton unless otherwise noted

Synonyms:

  • Dog-strangle vine
  • Cynanchum nigrum, Vincetoxicum nigrum

The Plant:

  • An herbaceous, perennial vine growing up to 6.5 feet long. Stems are unbranched but can twine around each other to form thick spirals.

The Leaves:

  • opposite
  • ovate or ovate-lanceolate
  • 2-5 inches long, 0.5-2.5 inches wide
  • dark green
  • entire
  • glabrous, shiny
  • short petioles

The Stem:

  • tough
  • twining
  • unbranched

The Flowers:

  • 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.

The Fruits:

  • slender
  • resemble narrow milkweed pods
  • green maturing to brown
  • seeds flat, brown, ovoid, membranous wing on margin
  • tuft of white hairs at one end

The Habitat:

  • woodlands, fields, roadsides, floodplains, uplands

Dispersal:

  • 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

Similar Species:

  • 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.

Notes:

  • 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

Origin: Europe

Level of Invasiveness for Nantucket: Invasive

Level of Invasiveness for Massachusetts: Invasive

Massachusetts Cultivation Restrictions: importation ban, propagation ban




Credits: The Electronic Field Guide to the Invasive Plants of Nantucket (c) 2005-2006 Maria Mitchell Association, EFG Project, UMass Boston