Pale swallow-wort flowers and leaves

Pale swallow-wort (Vincetoxicum rossicum)

Herbaceous, perennial vine that twines 3-6’ tall with small hairs on the stems and spreads vegetatively and reproductively. Dies back in the winter.

Overview

Regulated areas of pale swallow-wort
Pale swallow-wort is Prohibited (Red counties)

Other names for this plant include:

  • Common names: European swallow-wort
  • Scientific names: Cynanchum rossicum; C. medium; V. medium

Ecological threat:

  • Invades the understory of forests, woodland edges, grasslands, and old fields covering native vegetation and forming dense thickets. Tolerant of sun and shade.
  • Allelopathic.

Classification in Wisconsin: Prohibited

Species Assessment Groups (SAG) were assembled to recommend a legal classification for each species considered for NR 40. The recommendation for pale swallow-wort was based upon this literature review developed by the department.

Identification

Leaves: Opposite, oval, and smooth. Dark green and shiny with pointed tips and short petioles; 2-5” long.

Flowers: Pale swallow-wort has maroon to pale pink flowers and petals that are twice as long as wide and are hairless. Umbel-like, branched clusters have 6-10 flowers that bloom June-July.

Fruits & seeds: Slender pods, similar to milkweed, are 2-3” long, form late July-August, and turn from green to light brown or golden as they mature. Seeds are flat and attached to thin filaments that aid in wind dispersal, similar to milkweed.

Roots: Root crown fragments support dormant pale swallow-wort buds that resprout if not damaged. Does not have rhizomes; creeping perennial roots.

Similar species: Black swallow-wort (Vincetoxicum nigrum; invasive) is very much the same with the exception of the flowers. Black swallow-wort has dark purple flowers with petals that are the same length on all sides and are hairy.

Distribution

Known county distribution of pale swallow-wort
Counties in WI where pale swallow-wort has been reported (as of July 2011). Both vouchered and unvouchered reports included.

Currently, there have not been reports of pale swallow-wort in WI. Have you seen it? Send us a report.

Control

If the entire infestation cannot be treated focus on plants that are growing in the sun because they produce many more seeds than plants in the shade.

Mechanical: Remove all seed pods before they open and either burn or dispose of in a landfill; most effective if done in mid-July. If plants are dug up, all root fragments and root crown must be removed before seeds ripen.

Chemical: Cut-stem treatment with glyphosate. Foliar spray or wicking in August-September with either triclopyr ester or glyphosate and a surfactant after the infestation is mowed and new growth has formed. Foliar treatment should begin after flowering, but before seed production.

Photos

View pale swallow-wort pictures in our photo gallery!

Resources

Sources for content:

  • Czarapata, Elizabeth; Invasive Plants of the Upper Midwest: an illustrated guide to their identification and control. University of Wisconsin Press. 2005. Pg. 132-133
  • Plant Conservation Alliance's Alien Plant Working Group. Weeds Gone Wild: Alien Plant Invaders of Natural Areas. Pale Swallow-wort [exit DNR]

Links for More Information

Last revised: Wednesday December 19 2012