common milkweed, butterfly flower, silkweed, silky swallow-wort, Virginia silkweed

A. syriaca is a clonal perennial forb growing up to 1.8 m (5 ft 11 in) tall. Individual plants grow from rhizomes. All parts of common milkweed plants produce a white latex when cut. The simple leaves are opposite, sometimes whorled; broadly ovate-lanceolate. They grow to 10–28 cm (4–11 in) long and 4–12 cm (1+1⁄2–4+3⁄4 in) broad, usually with entire, undulate margins and reddish main veins. They have very short petioles and velvety undersides.

The highly fragrant, nectariferous flowers vary from white (rarely) through pinkish and purplish and occur in umbellate cymes. Individual flowers are about 1 cm (0.4 in) in diameter, each with five horn-like hoods and five pollinia. The seeds, each with long, white flossy hairs, occur in large follicles. Fruit production from self-fertilization is rare. In three study plots, outcrossed flowers had an average of about 11% fruit set.