What is a black swallow-wort?

Black Swallow-wort

_*Cynanchum louiseae*_

Family: Apocynaceae (dogbane)

Synonyms:

- Vincetoxicum nigrum

- Cynanchum nigrum

Description:

- Erect, perennial, herbaceous, twining vine with smooth, green to purplish, often glaucus (waxy-coated) stems.

- Leaves are arranged oppositely, simple, lanceolate-ovate to narrowly ovate in shape with smooth, entire (untoothed) margins and pointed tips.

- Small, dark purple flowers are borne in clusters (cymes) at branch ends and in upper leaf axils.

- Flowers have 5 petals that are fused at their base and reflexed at the tip, and 5 sepals that are much shorter than the petals.

- Fruit are cylindrical, smooth, paired seed pods that ripen from green to brown, split open lengthwise to release numerous shiny, black seeds that are attached to long white hairs.

Distribution:

- Native to Europe and Asia, introduced to the US as an ornamental around the 1850s.

- Currently occurs in 35 states in the Mid-Atlantic and northeastern US, as well as in British Columbia, Canada.

Impacts on natural areas:

- Black swallow-wort is a highly invasive species that forms dense monocultures in a wide range of habitats, including forest edges, thickets, fields, roadsides, and open disturbed areas.

- It is able to outcompete native plants for resources such as sunlight, water, and nutrients, leading to a reduction in native plant species diversity and loss of habitat.

- Its seed pods can be dispersed long distances by wind which allows it to quickly spread and colonize new areas.

- The species produces toxic compounds that can be harmful to wildlife and humans if ingested.

- It is unpalatable to most herbivores and provides little to no wildlife value other than being marginally valuable to a few pollinating insects such as bees and wasps.

Management:

- Early detection and rapid response are crucial to prevent the establishment and spread of black swallow-wort.

- Remove existing plants by carefully pulling them out by the roots.

- Cutting the plants can lead to further spread as the stem fragments are able to root and produce new plants.

- Dispose of plant material carefully to prevent any seeds from spreading.

- Monitor the site and remove any re-emerging seedlings.

- Use of herbicides may also be necessary in large infestations, following the recommendations on the herbicide label and state regulations.

- Biological control agents such as a gall midge and a flea beetle have been introduced and are being evaluated to help manage swallow-wort populations.

Prevention:

- Avoid planting black swallow-wort or any other invasive species.

- When purchasing nursery stock, be sure to inspect it carefully to avoid introducing invasive plants into your garden or landscape.

- Learn to identify invasive plants in your area and report any sightings to your local authorities.