Black Swallowwort (Cynachum louisea)

ABOUT THIS PLANT

Black swallowwort (Cynanchum louisea) originated in southern Europe and was likely imported as an ornamental. It first appeared in Massachusetts in 1864 where it was reported to have escaped from cultivation in Essex county. In the mid-1800's it was also cultivated at Harvard Botanical Garden. Today, it is in every country in Massachusetts.

HOW TO IDENTIFY

Leaf: The leaves are paired and opposite each other on the stem. They are ovular and/or heart shaped. The leaves are a dark green and grow 2-5 inches in length.

Fruit/Flower: The flower is a small, five petal dark blue or purple flower with triangular petals. The fruit is a 2-4 inch seed pod.

Growth form: Black swallowwort can be a low growing herbaceous forb as well as a climbing vine.

Black swallowwort looks very similar to Pale swallowwort (Cynanchum rossicum). Both plants are considered invasive. Pale swallowwort has pale purple flowers which tend to be smaller than Black swallowwort. Pale swallowwort is native to Ukraine and parts of Russia while Black swallowwort is native to the Mediterranean.
Above: Flower of Pale swallowwort (Cynanchum rossicum)
LIFE HISTORY
Flowering and Fruiting Period: Black swallowwort flowers from June to July. Its fruit, a seed pod called a follicle, appears soon after and persists to August. Once the seed pod bursts open, the seeds are wind-dispersed by tufts of feathery hairs that enable the wind to carry it.

Black swallowwort is classified as highly invasive. Research indicates that Monarch butterflies sometimes confuse Swallowwort species for Common milkweed (Asclepias syriaca) and lay their eggs on them. When the eggs hatch the caterpillars are unable to eat the leaves and starve.

REMOVAL

Black swallowwort roots may be easily pulled by hand. Pulling the plant in early spring, before flowering occurs, reduces the likelihood of the plant spreading. Depending on the size of the population, mowing 2-5 times per year may also be effective. For large populations, scarify the soil and seed with native grasses and forbs.