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Swallow-worts

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Common Name: Swallow-worts
Scientific Name: Cynanchum spp.
Origin: Europe

Description

Pale and black swallow-worts are herbaceous, perennial, twining vines. Their leaves are opposite and glossy, and their seed pods are smooth, slender and pointed, which are abundant in late summer. Pods split open, releasing innumerable downy seeds that are easily carried miles by wind. Pale and black swallow-worts are very similar and are hard to distinguish except by flower characteristics. Both species flower in late May through late August. Pale swallow-wort (Cynanchum rossicum) has small maroon to pale pink flowers with 5 hairless, triangular petals that are twice as long as they are wide. Black swallow-wort (Cynanchum louiseae) has small dark purple flowers with 5 pointed, downy, triangular petals that are the same length as their width.

Habitat

This plant will thrive in a wide range of soil, moisture and light conditions and is found in many habitats, including woodlands, fields and roadsides.

Threat

Swallow-wort vines choke out large areas of favorable species and can interfere with forest regeneration. Toxic chemicals in the plant make it poor forage for deer and other wildlife, including monarch butterflies which will sometimes lay their eggs on these plants, but their larvae do not survive.

Management

Individual plants or small infestations can be dug out by hand, although this appears to be more effective for black swallow-wort which has less robust roots. When cut, swallow-worts re-sprout vigorously, making mowing ineffective. Herbicides may be effective, however the milky sap within the plant make them less susceptible to herbicides. Multiple treatments over time will be necessary for control.

Distribution

Common