Setaria viridis (L.) P. Beauv.  

A tufted annual grass 10-40 (-60) cm tall. Leaf-blade 5-15 (-20) cm long,
4-12 (-18) mm wide; ligule a ciliate fringe. Panicle spicate, 2-5 (-12) cm long;
bristles antrorsely scabrid. Spikelets ellipsoid, 2-2.5 (-3) mm long; lower
Blume 1/4 to 1/3 the length of the spikelet, the upper as long as the spikelel;
Lower lemma sterile with a palea about 1/2 its length; upper lemma finely
rugose.