Parthenium hysterophorus L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Annual to 1 m, usually much branched, ± hairy, and often glandular above; lvs pinnatifid or usually bipinnatifid, to 2 × 1 dm; heads small, numerous in an often leafy infl, the disk 3–5 mm wide; achenes obovate, black, 2–2.5 mm; 2n=34. A weed of waste places; trop. Amer., n. to se. U.S. and occasionally to Mass., Mich., and Kans. July–Oct.