Asclepias tuberosa var. interior (Woodson) Shinners; A. tuberosa subsp. terminalis Woodson

Stems 30–90 cm. Leaf blades narrowly elliptic or lanceolate to oblong or linear, 2–12 × 0.5–3 cm, base obtuse or truncate to cordate, margins planar, apex acute to attenuate.

Flowering (Apr–)May–Sep(–Oct); fruiting Jun–Oct. Slopes, ridges, flats, valleys, streamsides, arroyos, can­yons, lake edges, cliffs, bluffs, dunes, sandhills, glades, fields, pastures, limestone, granite, sandstone, shale, sandy, silty, clay, gravel, and calcareous soils, prairies, shrubby grasslands, forest edges and openings, pine barrens, oak scrub, chaparral, oak, oak-hickory, and cedar woodlands, pine, oak, pine-oak, mixed-conifer, and riparian forests; 0–2500 m; Ont., Que.; Ala., Ariz., Ark., Colo., Conn., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.H., N.J., N.Mex., N.Y., N.C., Ohio, Okla., Pa., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., W.Va., Wis.; Mexico (Chihuahua, Coahuila, Nuevo León, Sonora, Tamaulipas).

Subspecies interior is one of the most widespread milkweeds and is distributed primarily west of the Appalachian Mountains, although there are scattered occurrences to the Atlantic Coast. Subspecies interior is rare and considered to be of conservation concern in Quebec (Pontiac County). Orange and yellow corollas predominate in the western states. R. E. Woodson Jr. (1953) established subsp. terminalis to accommodate northern and western peripheral populations bearing leaves with cuneate bases but subsequently returned these populations to subsp. interior (Woodson 1962).