Apocynum cannabinum L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Erect, branched above, 0.5–1.5 m, with a well developed main axis; lvs on short but evident petioles 3–10 mm, erect or ascending, 5–11 cm, oblong-lanceolate to oval or broadly elliptic, acute to rounded at the base and mucronate apex, glabrous or hairy beneath; fls erect; cal-lobes usually reaching beyond the middle of the cor-tube; cor cylindric to urceolate, 3–6 mm, white or greenish-white, the lobes erect or slightly divergent; fr (5–)10–15(–20) cm; coma mostly 1–3 cm; 2n=16. Open places; rare or local in e. Can. and N. Engl., abundant from N.Y. to N.D., s. to Fla. and Tex., and w. occasionally to the Pacific. May–Sept. Highly variable in lf-shape and pubescence.