Black Swallowwort

Cynanchum louiseae

Common Name: Black swallowwort (a.k.a. Climbing milkweed, Dog-strangling vine)
Scientific Name: Cynanchum louiseae
Family: Asclepidaceae
Growth Form: Herbaceous vine
Native Range: Europe
Alien Range: Northeastern United States and Canada
Introduction: Black swallowwort was introduced as an ornamental plant in the late 1800s.  It has since escaped from cultivation and spread by seed.
Description: ·Leaves:  Simple, opposite, smooth, entire margins.  5-10 cm (2-4 in.) Oblong or ovate in shape.  Dark green.

·Stem:  Smooth, un-branched.  Can wind around other plants and trees, growing 1-2 m (3-6 ft.) long.

·Flowers:  Purple-black corolla of 5 lobes.  Lobes thick and triangular with fine white hairs.  Inflorescences of 6-10 flowers occur at leaf axils from .5-1.5 cm stalks.  Present from June to September. 

·Fruit: Paired, dark brown pods.  4-7 cm (2-3 in.) long. Thin, elliptical shape.    Flat, brown, elliptical seeds.  5-7 mm long.  Tuft of fine hair at one end.
Threats: Forms dense stands in disturbed areas such as Christmas tree plantations, nursery crops, alfalfa and conservation habitats.  Shades out native vegetation, reduces biodiversity, can strangle trees and shrubs as it winds around them.
Fun Facts: Butterflies generally lay eggs in members of the milkweed (Asclepidaceae) family, but the eggs cannot survive in black swallowwort because of the plant’s toxicology.
Whole plant
Whole plant