florida Early Detection Network


Black Swallow-wort, Dog-strangle Vine


Cynanchum louiseae Kartesz & Ghandi


Milkweed family


Cynanchum louiseae

Comparision of flowers of
Cynanchum louiseae (top)
and Cynanchum rossicum (bottom)

Close-up of fruit



Close-up of flowers

Twining vines


Dehiscing seeds


Synonyms: Vincetoxicum nigrum (L). Moench, Cynanchum nigrum (L.) Pers. non Cav.


Botanical Glossary

Cynanchum louiseae is an herbaceous, perennial vine, growing up to 2 m (6.5 ft.) in length. It has an unbranched and twining habit. Its dark green leaves are opposite and have entire margins, are glabrous and shiny, and have short petioles. The leaves are ovate or ovate-laceolate in shape, are 5-13 cm (2-5 in.) long and 1.25-6 cm (0.5-2.5 in.) wide. Clusters of 6-10 flowers are produced in opposite, axillary cymes from June to September; peduncles are 0.5-3 cm (0.2-1.2 in.) long. The 5-lobed corolla is dark purple in color. The fleshy corolla lobes are shaped like an equilateral triangle, 1.5-3 mm (0.05-0.1 in.) in length, with short straight, white hairs on the upper surface. A minutely toothed corona is weakly 5-lobed, its segments joined by a connective membrane that is 2/3 the height of the corona. Fruits are slender, elliptical follicles, 4-7 cm (1.5-2.75 in.) in length, similar to that of milkweed but narrower. Immature pods are green, turning brown with maturity. Seeds are brown, flattened, 5-7 mm (0.2-0.3 in.) in length and ovoid. They have a membranous wing along the margin and a tuft of white hairs at the narrow end. Stems persist at the end of the season, frequently bearing open pods with some seeds remaining inside. Page References Fernald 1176, Gleason & Cronquist 399, Holmgren 374, Magee & Ahles 845, Newcomb 326, Peterson & McKenny 390. See reference section below for full citations.


Cyanchum rossicum (Kleopov) Barbarich (Pale swallow-wort)/p>


The seeds of Cynanchum louiseae are dispersed primarily by wind. If they fall into moving water they float and are transported downstream.


Cynanchum louiseae is native to Europe where it occurs in different habitats than the very similar C. rossicum. In Canada, Cynanchum louiseae has been reported from Quebec and Ontario. In the United States its range extends from the Atlantic coast to the mid west and as far south as Kentucky and Missouri. It is present in all New England States.


Although its history of introduction is uncertain, the first record for Cynanchum louiseae is from Camrbidge, Massachusetts (Middlesex County) where it was collected in 1878. It may have come from the Harvard Botanic Garden. Cynanchum louiseae either subsequently spread throughout New England or was planted elsewhere: there are early records from Rhode Island and Vermont in 1880 and Connecticut and Maine in 1901.


Abandoned Field, Early Successional Forest, Edge, Floodplain Forest, Forest Wetland, Pasture, Planted Forest, Roadside, Utility Right-of-Way, Vacant Lot, Wet Meadow, Yard or Garden. Cynanchum louiseae can be found in many habitats, including woodlands, fields, and along roadsides, floodplains, urban areas and utility rights-of-way. It grows well in almost any upland situation.


Cynanchum louiseae is a vine that can grow rapidly and cover native vegetation. It also has the ability to dominate the understory of a woodland. Wind-dispersed seeds allow it to disperse over long distances. When it is cut, this plant resprouts vigorously, making control difficult.


Documentation required: Specific photograph or mounted snippet of the stem with flowers. Best time for documentation: Late spring, summer.


Rhode Island Coooperative Agriculture Pest Survey and National Agricultural Pest Information System - Brief discription of C. louiseae and control measures

Integrated Taxonomic Information System - Taxonomic information about the species

The PLANTS database - General information and map


Brown, W.T., M.E. Krasny and N. Schoch. 2000. Volunteer monitoring of nonindigenous invasive plant species in the Adirondack Park, New York, USA. Natural Areas Journal 21 (2): 189-196.

Fernald, M.L. 1950. Gray's Manual of Botany 8th ed. American Book Co., Boston.

Gleason, H.A. and A.C. Cronquist. 1991. Manual of Vascular Plants of the Northeastern United States and Adjacent Canada. 2nd ed. New York Botanical Garden, Bronx, New York.

Holmgren, N.H. 1998. Illustrated Companion to Gleason and Cronquist's Manual. New York Botanical Garden, Bronx, New York.

Lumer, C. and S.E. Yost. 1995. The Reproductive-Biology Of Vincetoxicum nigrum (L) Moench (Asclepiadaceae), A Mediterranean Weed In New-York-State. Bulletin Of The Torrey Botanical Club 122 (1): 15-23.

Magee, D.W and H.E. Ahles. 1999. Flora of the Northeast. University of Massachusetts Press, Amherst.

Newcomb, N. 1977. Newcomb's Wildflower Guide. Little Brown, Boston.

Peterson, R.T. and M. McKenny. 1968. A field Guide to Wildflowers of Northeastern and North-central North America. Houghton Mifflin, Boston.

Sheeley, S.E. and D.J. Raynal 1996. The distribution and status of species of Vincetoxicum in eastern North America. Bulletin Of The Torrey Botanical Club 123 (2): 148-156.