Ambrosia acanthicarpa Hook.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Branching annual 1–8 dm, coarsely strigose to scabrous-hispid or both; lvs petioled, opposite below, alternate above, bipinnatifid (or the upper sessile and once pinnatifid), the blade 2–8 cm; heads numerous in terminal-racemiform clusters, sometimes chiefly staminate or chiefly pistillate; fruiting invols solitary or clustered in the upper axils, 5–10 mm, 1- fld and 1-beaked, with several series of flattened, divergent spines, these sometimes reduced in the chiefly staminate plants; 2n=36. Open places, especially in sandy soil; Wash. to Calif., e. to Sask. and Tex., and occasionally intr. eastward, as in Minn. and Mo. July–Oct. (Franseria a.; Gaertneria a.)