Setaria verticillata (L.) P.Beauv.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Annual 3–10 dm, scabrous just beneath the infl; sheaths ciliate- margined above; blades flat, 10–25 cm × 5–15 mm, scabrous on both sides, sometimes also with scattered hairs above; infl erect, yellow-green or purplish, 5–15 cm, cylindric but lobulate, the branches verticillate, the axis scabrous-hispid on the angles, not villous; bristle one below each spikelet, 4–7 mm; spikelets 2–2.2 mm; first glume 1(–3)-veined, a third as long as the spikelet, the second 5-veined, nearly as long as the spikelet; sterile lemma nearly as long as the spikelet, clasping a rather broad palea half as long; fertile lemma transversely finely rugulose; 2n=36. Native of the Old World, now widespread in N. Amer. as a weed in gardens and greenhouses, and along the banks of streams and irrigation-ditches. Var. verticillata has the bristles retrorsely scabrous, and the axis of the panicle is retrorsely scabrous-hispid. The much less common var. ambigua (Guss.) Parl. has the bristles and panicle-axis antrorsely instead of retrorsely scabrous. (S. viridis var. ambigua)