MADISON, Wis. – The Wisconsin Department of Natural Resources today announced the confirmed presence of pale swallow-wort (Vincetoxicum rossicum), an invasive vine, in Oconto and Shawano counties.
The vine was found within the outskirts of the town Krakow along the shared county line. These are the first known populations in the state, making rapid response efforts critical to preventing the establishment of this species in Wisconsin.
The sites were first reported by the Timberland Invasives Partnership via the Early Detection and Distribution Mapping System (EDDMapS), an online invasive species reporting tool. These reports were subsequently brought to the attention of the DNR. The Timberland Invasives Partnership is a non-profit organization focused on controlling and raising awareness about invasive species in Langlade, Menominee, Oconto and Shawano counties.
Despite not having tendrils, this invasive vine twines and grows on top of surrounding vegetation, resulting in the displacement of native species in forests and grasslands. Both pale swallow-wort and its close relative, black swallow-wort (V. nigrum; also invasive), are within the milkweed family (Apocynacae) and can outcompete native milkweed. Monarch butterflies have been observed laying eggs on swallow-wort, but once they hatch, the caterpillars can’t survive on these non-native milkweed relatives. Learn more about pale and black swallow-wort.
Due to these impacts, pale swallow-wort is classified as a prohibited invasive species in Wisconsin. Invasive species are not native and cause harm to Wisconsin’s environment, economy or pose threats to human health. To help prevent the introduction and spread of invasive species, the department established Wisconsin’s Invasive Species Rule (ch. NR 40) in 2009 (last revised, 2015). Under the rule, it is unlawful to transport, transfer, introduce or possess prohibited species in Wisconsin.
The leaves of pale swallow-wort occur opposite of each other along the stem and are oblong-to-oval in shape with a pointed tip, smooth edges, are light to dark green in color and can sometimes appear glossy. Slender seedpods, resembling those of milkweed plants, appear from mid to late summer. The flowers are the best key diagnostic feature and will help distinguish pale from black swallow-wort. For both plants, the flowers are star shaped with five petals and appear in clusters where the leaf connects to the stem (the axil). Pale swallow-wort flower petals are smooth on top, are longer and tapered and pinkish or light brown in color. Black swallow-wort petals are triangular, hairy on top and dark purple or blackish in color.
If you believe you have found pale swallow-wort, please report it to Invasive.Species@wisconsin.gov. All reports should include the location and clear photos of the plant’s identifiable features. Other important details such as population size and landownership are also encouraged. If preferred, the public may also submit a report using the EDDMapS.
The DNR continues to work with the Timberland Invasives Partnership, landowners and additional partner organizations in the area to raise awareness and coordinate plant control efforts. This collaborative approach helps ensure additional populations can be found and controlled before this species can become established.
