Swamp milkweed

Stems 70–150 cm, puberulent in a line with curved trichomes to glabrate. Leaves: petiole 7–15 mm, pilosulous; blade lanceo­late to linear-lanceolate, 5–15 × 0.5–4 cm, surfaces sparsely puberulent with curved tri­chomes, more densely on veins, to glabrate. Peduncles puber­ulent with curved trichomes to pilosulous, sometimes only on 1 side. Pedicels pilosulous to puberulent with curved trichomes, sometimes only on 1 side. Flowers: corolla bright pink to white; corona pink to white, paler than corolla; anthers green to brown. 2n = 22.

Flowering (Apr–)Jun–Sep; fruiting Jul–Nov. Marshes, swamps, creeks, ditches, wet depressions, streamsides, pond edges, sandhills, dolomite, limestone, saturated and sandy soils, riparian woods, mixed hardwood for­ests, hammocks, wet meadows and prairies, pastures; 0–1700 m; Man., N.B., Ont., Que.; Ala., Ariz., Ark., Colo., Conn., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Pa., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., W.Va., Wis., Wyo.; Mexico (Coahuila).

Subspecies incarnata is most common west of the Appalachian Mountains and is the only one commonly found in Florida. It has several, disjunct occurrences in wetlands in the Rocky Mountain and Intermountain states and notably along the Snake River in Idaho. It would be interesting to determine whether these occur­rences represent relictual populations, recent dispersals (introductions?), or a combination of these. Subspecies incarnata is considered rare in Arizona (Santa Cruz County), Louisiana (Jefferson, LaFourche, St. Charles, Terrebonne, and Vernon parishes), and Montana (Carbon County). Genotypes of this subspecies are the source of several widely available cultivars, including one with pure white flowers.