The Urban Pantheist

Location: Price Road, Allston.

Urban species #160: Black swallow-wort Cynanchum nigrum

Tiny star-shaped flowers , so dark purply-brown they look black, are the primary charm of this weed. Later in the season it develops pods that release seeds that float on silken parachutes (similar to, but more restrained than, cottonwood). It twines up chain-link, putting glossy dark green green foliage on ugly fences. Its attractiveness cause it to be introduced to North America as an ornamental. Unfortunately, there is little else that is positive about this plant, at least as it exists outside of its native range of Eastern Europe.

It is strongly invasive, and has several deleterious effects. Like other members of the milkweed family, it is poisonous. So when it crawls in among crops or pasture fields, it makes mechanical harvesting impossible, and whole pastures unusable by livestock. When it invades grasslands, there is a population drop among birds that nest in such areas. Monarch butterflies recognize it as a milkweed, and lay their eggs on it, but their larva are unable to feed on it, and starve. It joins garlic mustard and Japanese knotweed on the "least wanted" list, for New England native plants enthusiasts.