Cynanchum louiseae, Black Swallowwort

Gardens & Landscapes, Invasive Species, Extension Master Gardener December 16, 2015 Print Friendly and PDF

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.

Black dog-strangling vine, black swallowwort Black dog-strangling vine, black swallowwort
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.

Black dog-strangling vine, black swallowwort Black dog-strangling vine, black swallowwort
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.

Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Black dog-strangling vine, black swallowwort
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.

Black dog-strangling vine, black swallowwort Black dog-strangling vine, black swallowwort
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.

honeyvine swallowwort honeyvine swallowwort
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

wavyleaf twinevine wavyleaf twinevine
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


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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.