Bidens bipinnata L.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Glabrous or minutely hairy annual 3–17 dm; lvs 4–20 cm including the 2–5 cm petiole, mostly 2–3 times pinnately dissected, the ultimate segments tending to be rounded; heads narrow, disciform, the disk only 4–6 mm wide at anthesis, the short, ochroleucous rays not surpassing the disk; outer invol bracts 7–10, linear, ± acute, not evidently expanded upwards, shorter than the inner; achenes linear, tetragonal, narrowed above, often sparsely hairy, 10–13 mm, or some of the outer shorter; pappus of (2)3 or 4 yellowish awns; 2n=24, 72. Moist to fairly dry, disturbed habitats; Mass. to Fla., w. to Neb., Calif., and Mex., e. Asia. July–Oct.