Asclepias tuberosa, commonly known as butterfly weed, is a species of milkweed native to eastern and southwestern North America. It is commonly known as butterfly weed because of the butterflies that are attracted to the plant by its color and its copious production of nectar.

It is a perennial plant growing to 0.3–1 m (1–3+1⁄2 ft) tall. The leaves are spirally arranged, lanceolate, 3–12 cm (1+1⁄4–4+3⁄4 in) long, and 2–3 cm (3⁄4–1+1⁄4 in) broad.

From April to September, in the upper axils, 7.5 cm (3 in)–wide umbels of orange, yellow or red flowers 1.5 cm (1⁄2 in) wide appear. They each have five petals and five sepals. It is uncertain if reddish flowers are due to soil mineral content, ecotype genetic differentiation, or both. A cultivar named "hello yellow" typically has more yellowish flowers than ordinary examples of this plant.

The fruit pod is 7.5–15 cm (3–6 in) long, containing many long-haired seeds.

The plant looks similar to the lanceolate milkweed (Asclepias lanceolata), but is uniquely identified by the larger number of flowers, and the hairy stems that are not milky when broken. It is most commonly found in fields with dry soil. Tropical milkweed (Asclepias curassavica) can resemble Asclepias tuberosa in its red form but also lacks hairy stems.

Common names include butterfly weed, Canada root, chieger flower, chiggerflower, fluxroot, Indian paintbrush, Indian posy, orange milkweed, orange root, orange swallow-wort, pleurisy root, silky swallow-wort, tuber root, yellow milkweed, white-root, windroot, butterfly love, butterflyweed, and butterfly milkweed.

The species can be found from South Dakota south to Texas and Mexico, west to Utah and Arizona, as well as many other areas further east.

This plant favors dry, sand or gravel soil, but has also been reported on stream margins. It requires full sun.