Asclepias syriaca L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Colonial by roots; stems stout, 1–2 m, mostly simple, hairy; lvs thick, narrowly or broadly elliptic to ovate or oblong, 10–15 cm, acute or apiculate, soft-hairy beneath; petioles 5–15 mm; umbels often numerous, terminal and lateral, compactly many-fld; peduncles 3–10 cm; cor nearly purple to nearly green, its lobes 7–10 mm; hoods pale purple, somewhat divergent, 4–5 mm, surpassing the gynostegium, the lateral margins with a prominent, sharp, triangular lobe near the middle; horns short, inflexed; fr erect on deflexed pedicels, 7–12 cm, tomentose and beset with soft, filiform to conic processes; 2n=22. Fields, meadows, and roadsides; N.B. to Va. and n. Ga., w. to Man., Nebr., and Okla. June–Aug. (A. kansana) Native, the specific epithet in error.