Common Milkweed

Asclepias syriaca

Weed Description
Perennial, erect, from a deep rhizome that excretes a milky sap when broken. Found throughout the northeastern United States, south to Virginia and northern Georgia, and west to the Rocky Mountains.

Seedlings
Cotyledons flat, dull green, oval (1.2 cm long), plants emerging from rhizomes lack cotyledons and are much more robust than seedlings.

Leaves
Opposite, with an untoothed margin (entire), oblong to oval, 10-30 cm long, 5-11 cm wide, petiolated. Lower leaf surfaces finely pubescent, while the upper surface is without hairs (glabrous).

Stems
Rarely branched, erect, hollow, covered with fine hairs, emitting a milky sap when broken. Stems green initially but may become red with maturity.

Flowers
In clusters (umbels) of 20-130 at the end of stems and in the upper leaf axils, greenish-purple to greenish-white. Each flower is on a long, slender stalk.

Fruit
Follicles that are large (8-13 cm long), teardrop-shaped, grayish-green and hairy. Each follicle may contain many seeds that are 6-10 mm long, flattened, brown, with a papery margin and a tuft of silky hairs.

Roots
Taproot with a deep rhizome.

Identifying Characteristics
All parts of the plant excrete a milky sap when broken. Hemp Dogbane (Apocynum cannabinum) is often confused with common milkweed, especially at emergence. However, much smaller leaves and greater degree of branching in hemp dogbane help to distinguish this weed from common milkweed.

Office of Programs

University of Missouri

Common Milkweed

Asclepias syriaca