6b. Bristles 1-3 at the base of each spikelet --7. 7a. Spikelets about 2 mm. long; bristles not much longer, green =Green Foxtail, Setaria viridis.= 7b. Spikelets about 3 mm. long; bristles much longer, usually purple =Millet, Setaria italica.= 8a. Spikelets numerous, in long slender symmetrical spikes --9. 8b. Spikelets in panicles, racemes, or loose spikes --13. 9a. Spikelets without awns; plants 8 dm. high or less (Crab Grass) --10. 9b. Spikelets with awns; plants 12 dm. high or more --12. 10a. Leaf-sheaths all glabrous. =Crab Grass, Digitaria humifusa.= 10b. Lower leaf-sheaths hairy --11. 11a. Axis of the spike flat, with wing-like margins =Crab Grass, Digitaria sanguinalis.= 11b. Axis of the spike slender, without winged margins =Crab Grass, Digitaria filiformis.= 12a. Spikes numerous, appressed to the axis of the panicle; tall marsh grass =Slough Grass, Spartina michauxiana.= 12b. Spikes 2-6, widely divergent; plant of dry ground =Blue-joint, Andropogon furcatus.= 13a. Spikelets subtended by an ovoid thorny involucre 3-8 mm. wide =Sand Bur, Cenchrus carolinianus.= 13b. Spikelets without a thorny involucre --14. 14a. Lower branches of the panicle spreading, bearing staminate flowers, the upper branches erect, with pistillate flowers; aquatic or marsh grass 2-4 m. high =Wild Rice, Zizania aquatica.= 14b. Panicle uniform throughout --15. 15a. Spikelets with awns 2 mm. or more long --16. 15b. Spikelets not awned, or with short inconspicuous awns --18. 16a. Spikelets in solitary raceme-like spikes; awn about 1 cm. long or more =Beard Grass, Andropogon scoparius.= 16b. Spikelets in branching clusters; awn less than 1 cm. long --17. 17a. Leaf-blade 4 mm. wide or narrower; panicle slender =Drop-seed, Muhlenbergia schreberi.= 17b. Leaf-blade 6 mm. wide or more; panicle stout and coarse =Barnyard Grass, Echinochloa crus-galli.= 18a. Spikelet plump and compact, its bracts closely folded about each other --19. 18b. Spikelet very flat, its two bracts closely folded together =Cut-grass, Leersia oryzoides.= 18c. Spikelet loose and open, somewhat flattened, its 3 bracts ascending or spreading and not closely folded about each other --20. 19a. Panicle about half as long as the entire plant; leaves copiously hairy =Witch Grass, Panicum capillare.=