Invasive Species: Cynanchum louiseae, Black Swallowwort
Black swallowwort is an invasive herbaceous, twinning, perennial vine. Leaves are opposite, dark green, oval, shiny, entire, 3 to 4 in. (7.6 to 10.2 cm) long, and 2 to 3 in. (5.1 to 7.6 cm) wide. Flowering occurs in June to July when dark purple, five-petaled, star-shaped flowers appear in clusters. Flowers are approximately 0.25 in. (0.6 cm) across and covered with white hairs. Fruit are pods, similar to milkweed pods, which are slender, 2 to 3 in. (5.1 to 7.6 cm) long, and split to reveal small seeds with tufts of white hair. The hair allows the seeds to be readily dispersed. Plants have rhizomes that sprout new plants. Black swallowwort invades upland areas with a wide range of light and moisture conditions. Black swallowwort is native to Europe and escaped from a botanical garden in Massachusetts.
What are invasive species and why should we be concerned about them?
Taxonomy: Scientific and Common Names for This Species
Gentianales > Asclepiadaceae > Cynanchum louiseae Kartesz & Gandhi
Synonym(s): Louis’ swallow-wort
Cynanchum louiseae – USDA PLANTS Profile
Distribution Maps
Black swallowwort – The reported distribution of this invasive species across the United States. (Source: Invasive Plant Atlas of the United States)
Up-to-the-minute distribution maps and why they are important
Reporting This Invasive Species
What is the best way and place to report the occurrence of an invasive species?
How to report an invasive species sighting to EDDMapS – Early Detection & Distribution Mapping System
EDDMapS – Report an invasive species to EDDMapS
Cooperative Extension Offices – Find your local Cooperative Extension office on this map provided by USDA
How to Identify
This invasive species can be identified by looking for the characteristics described in the paragraphs that follow.
Vine
Black swallowwort is an invasive herbaceous, twinning, perennial vine.
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| Leslie J. Mehrhoff, University of Connecticut, bugwood.org | Leslie J. Mehrhoff, University of Connecticut, bugwood.org |
Foliage
Leaves are opposite, dark green, oval, shiny, entire, 3 to 4 in. (7.6 to 10.2 cm) long, and 2 to 3 in. (5.1 to 7.6 cm) wide.
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| Leslie J. Mehrhoff, University of Connecticut, bugwood.org | Leslie J. Mehrhoff, University of Connecticut, bugwood.org |
Flower
Flowering occurs in June to July when dark purple, five-petaled, star-shaped flowers appear in clusters. Flowers are approximately 0.25 in. (0.6 cm) across and covered with white hairs.
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| Leslie J. Mehrhoff, University of Connecticut bugwood.org | Leslie J. Mehrhoff, University of Connecticut, bugwood.org |
Fruit
Fruit are pods, similar to milkweed pods, which are slender, 2 to 3 in. (5.1 to 7.6 cm) long, and split to reveal small seeds with tufts of white hair.
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| Leslie J. Mehrhoff, University of Connecticut, bugwood.org | Leslie J. Mehrhoff, University of Connecticut, bugwood.org |
Native Species That Resemble Black Swallowwort
Cynanchum laeve, honeyvine swallowwort – Images at invasive.org
This species is native to the United States but can be considered nonnative to areas of Canada.
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| Ohio State Weed Lab Archive, The Ohio State University, bugwood.org | Dan Tenaglia, Missouriplants.com, bugwood.org |
Funastrum crispum, Funastrum crispum – Images at invasive.org
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| Karan A. Rawlins, University of Georgia, bugwood.org | Karan A. Rawlins, University of Georgia, bugwood.org |
Additional Images for Black Swallowwort
Black swallowwort – Images at Invasive.org
Learning Resources for Black Swallowwort
Cynanchum louiseae Identification Card – U.S. Fish & Wildlife Service
Cynanchum louiseae Fact Sheet – U.S. Fish & Wildlife Service
Additional Information, Biology, Control and Management Resources
Control and management recommendations vary according to individual circumstances. Location, habitat, weather, and a variety of other conditions are factors that help determine the best treatment choice. To find the safest and most effective treatment for your situation, consult your state’s land-grant institution. If you will use chemicals as part of the control process, always refer to the product label.
United States Land-Grant University System – Find your land-grant university’s College of Agriculture, Cooperative Extension Service, or other related partner on this map provided by USDA.
Plant Invaders of Mid-Atlantic Natural Areas – National Park Service and U.S. Fish and Wildlife Service
Biological Control of Invasive Plants in the Eastern United States – USDA Forest Service
Invasive Plant Atlas of New England – University of Connecticut
Element Stewardship Abstract – The Nature Conservancy
Weed of the Week – USDA Forest Service
Weeds Gone Wild: Alien Plant Invaders of Natural Areas – Plant Conservation Alliance