Asclepias perennis Walter
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Stems slender, often branched, 4–8 dm, pubescent in narrow lines; lvs thin, lanceolate to narrowly elliptic, 5–14 cm, gradually tapering at base into a conspicuous petiole; umbels solitary or few; cor white, the lobes 3–4 mm; hoods and horns as in no. 3 [Asclepias incarnata L.], 2–3 mm; seeds without a coma. Swamps and wet woods; s. coastal plain from S.C. to Tex., n. in the Mississippi and Ohio valleys to s. Mo. and s. Ind. July, Aug.