5 



9a. Spikelets without awns; plants 8 dm. high or less (Crab Grass) 



10. 

 9b. Spikelets with awns; plants 12 dm. high or more 12. 



lOa. Leaf-sheaths all glabrous. Crab Grass^ Pigitaria humifusa. 

 1Gb. Lower leaf-sheaths hairy 11. 

 lla. Axis of the spike flat, with wing-like margins 



Crab Grass, Bigitaria sanguinalis. 

 lib. 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 Slougli Grass, Spartina michauxiaiia, 



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, Cenehrus curolinianus. 

 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 I 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 op.en, 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. 



19b. Panicle of smaller size 



Panic-grasses, yarious species of Panicum. 



20a. Panicle strongly contracted or spike-like; plants of sand- 

 dunes - 4a. 



20b. Panicle spreading or slightly contracted; axis of the spike- 

 let beset with bristles; leaves 2 dm. long or more; marsn 

 grass Reed Grass, Calamagrostis canadensis. 



20c. Panicle spreading or somewhat contracted, but not spike- 

 like; axis of the spikelet without bristles 21. 



