Black Swallowwort, Vincetoxicum nigrum also called “Dog Strangling Vine”, is an invasive vine native to south eastern Europe. Black Swallowwort was introduced to New England in 1854 as an ornamental plant.
Black Swallowwort is closely related to common milkweeds ( Asclepius species) which are native to North America. Black Swallowwort is more toxic than milkweeds, making it hazardous to grazing animals like deer and cattle. Due to its relation to milkweeds, Monarch Butterflies are also known to lay there eggs on it but the larvae cannot survive on it. Black Swallowwort is currently throughout the Northeastern United States as well as Eastern Canada.
Black Swallowwort has unbranching stems which can grow to 6 feet in a single season with long, dark green, oval shaped leaves, which can be 2-4 inches long, grow opposite each other on the stem. Black Swallowwort produces clusters of small deep purple to black star shaped flowers approximately 1/4 inch in diameter, when pollinated these flowers produce seed pods which measure 1.5-3 inches long. The vine produces a dense, woody taproot, and a fibrous mass of roots which can lead to asexual spreading but primarily are used for regeneration from year to year, but also production of new stems.
New stems of V.nigurm sprout in the spring, flowering begins in late May, peaking during late June but will continue until mid-July. Seed pods mature and begin to release seeds in mid-August and can continue until late October. The seeds are primarily wind dispersed, carried by a parachute like structure called a coma which is comprised of silk like fibers. The seeds can also cling to animals and to clothing for dispersal. The winter frost will cause the stems to dieback but the plant will survive through seeds and the woody taproot.
Black Swallowwort can be found in numerous locations most notably fields (agricultural and natural) and the edges of forested areas, preferentially growing in full sun but also in partial shade.