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More invasives: Pale Swallow-wort

While the foot of West Hill is threatened by the aquatic plant Hydrilla, up on the slopes a very serious invasion comes from the pale swallow-wort, a Euroopean that has gained a foothold in New York State. We’ll be posting details about where it has been found and what we can do about it. For now, here is the introductory information, taken verbatim from the Plant Conservation Alliance’s Alien Plant Working Group. Their complete report is at Pale Swallow-Wort where you’ll find details including various management options. A PDF version (exactly the same info) of the complete report: Pale Swallow-Wort PDF

Pale Swallow-Wort

Cynanchum rossicum (Kleopov) Barbarich
Milkweed family (Asclepiadaceae)

Pale Swallow-wortNATIVE RANGE



Pale or European swallow-wort (previously Vincetoxicum rossicum) is a long-lived perennial, twining herbaceous vine. The leaves are oval shaped with pointed tips, 3-4 in. long by 2-3 in. wide, and occur in pairs along the stem. The small five-petaled, star shaped flowers are creamy pink to reddish brown, about ¼ in. across, and are borne in clusters. The fruits are slender tapered pods, 2-3 in. long by about ¼ in. wide, that turn from green to light brown as they mature. When ripe, the fruits open along a seam and release flattened seeds equipped with a downy parachute that aids in wind dispersal. In contrast to its invasive relative the black swallow-wort (C. louiseae), pale swallow-wort does not have rhizomes. Plants tend to grow in clumps of several to many stems, forming extensive patches.

NOTE: There are many native species of Cynanchum, including honeyvine (Cynanchum laeve) which occurs throughout the eastern U.S. and could be confused with pale swallow-wort. Honeyvine has white flowers, and its leaves have a distinct heart-shaped base.


Pale swallow-wort can form extensive patches that crowd out native plant species and have various impacts on native wildlife. In some instances old-field habitats occupied by goldenrods and grasses are replaced almost exclusively by swallow-wort, disrupting natural succession and completely altering the physical structure of those habitats. A New York study on grassland birds indicated that as swallow-wort cover increases, grassland bird presence declines. In a study of ground and stem-dwelling insects in Ottawa, Ontario, diversity of these insects was found to be lower in pale swallow-wort infestated areas than in non-invaded old-field sites and gall-makers and miners were completely absent. In New York, pale swallow-wort is displacing the federally listed Hart’s tongue fern (Asplenium scolopendrium) at one site and poses a threat to additional populations in the state. Globally rare alvar habitats (limestone pavement barrens supporting unique plant communities) in New York are also threatened by expanding swallow-wort populations. Research indicates that pale swallow-wort modifies the soil microbial community, displacing native plant species that are adapted to the unique microbial associations of alvar.

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