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Have you seen swallow-wort vine?

June 12, 2012
BY HILARY SMITH ( , Adirondack Daily Enterprise

The field season is here and the hunt for invasive plants is underway. Crews, volunteers and concerned citizens have eyes open for new infestations. The best time to detect invasive plants is when they are in flower.

One plant in full bloom right now is yellow iris (Iris pseudacorus), a showy ornamental plant from Eurasia that invades shorelines and wetlands. It has exploded in popularity as a garden favorite in recent years, but plants don't stay put. One clump becomes three, then 10. One of the largest infestations in our region covers 4 acres. At this size, elimination is unlikely.

Detecting plants early is critical. The sooner we find an infestation the more likely it is that we can successfully eliminate it.

Article Photos

Pale swallow-wort has star-shaped, creamy pink to reddish brown, 5-petaled flowers. Black swallow-wort is similar but has dark purple to black flowers.
(Photo courtesy John M. Randall, The Nature Conservancy,

We need your help to identify another invasive plant that will soon be in bloom. Swallow-wort vine is widespread throughout central and western New York but just starting to make in-roads into our region. Time is of the essence to find new locations of this swiftly spreading plant.

Last summer, our field crews found, and treated, the first infestation of swallow-wort in the southwestern Adirondacks. And several infestations are just beyond the Park's western boundary. This is cause for concern.

Ecological impacts are severe, and management is costly. Infestations smother native vegetation, degrade grassland bird habitat, disrupt soil microbial communities and reduce insect diversity. Rapidly expanding populations in Jefferson County are putting at risk federally endangered plants and globally rare habitats.

A member of the milkweed family, swallow-wort produces seeds that can be easily dispersed long distances by wind. Finding new infestations can be tricky since small populations - when elimination is easiest - could go un-noticed. Extra vigilance to search for this plant will be required to hold the line of its spread.

Both black swallow-wort (Cynanchum louiseae) and pale swallow-wort (C. rossicum) are perennial, twining vines native to Europe. Look for oval shaped leaves with pointed tips, 3 to 4 inches long by 2 to 3 inches wide that occur in pairs along the stem. Small, five-petaled, star-shaped flowers are one-fourth-inch across, borne in clusters and bloom in June and July. Black swallow-wort has dark purple to almost black flowers with white hairs, and pale swallow-wort has creamy pink to reddish brown flowers.

The fruits are slender tapered pods, 2 to 3 inches long by about one-fourth-inch wide, turning from green to light brown as they mature. When ripe, the fruits open and release flattened seeds equipped with downy parachutes that aid in wind dispersal. Thick infestations in full sun can produce 2,000 seeds per square meter. Wind dispersal of seed begins in late July to early August and continues throughout late summer and fall.

Swallow-wort tolerates a range of light, moisture and salt conditions. Typical habitats include old fields, hedgerows, brushy areas and the ground layer of woodlands. Both natural and human-caused disturbance including ice-scoured river banks, rocky slopes, transportation corridors, quarries and abandoned agricultural fields provide acceptable habitats.

Please be on the lookout for swallow-wort vine. Here is the line-up of locations where it is known: Elizabethtown along the Boquet River; Willsboro on one property along the shores of Lake Champlain; Malone along the Salmon River; town of Ohio along Farr Road; and Ticonderoga on one private property.

If you think you see swallow-wort, take note of its location and a photo if possible. Report sightings to Brendan Quirion, Terrestrial Project Coordinator for the Adirondack Park Invasive Plant Program, at 518-576-2082 ext. 118 or

Thank you for your help.


Eye on Invasives is a biweekly column that spotlights a top invader when it is easiest to identify. Hilary Smith directs the Adirondack Park Invasive Plant Program, a partnership program housed at the Adirondack Chapter of The Nature Conservancy in Keene Valley. Find out more about this award-winning program online at



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