3c. Bracts of the spikelet without terminal awns, but the spikelets with one or more long bristles arising from their base --6.
4a. Spike-like panicle thickened in the middle, more than 1 cm.
thick =Beach Gra.s.s, Ammophila arenaria.=
4b. Spike little or not at all thickened in the middle, less than 1 cm. thick --5.
5a. Lower bracts awned; stem erect, unbranched =Timothy, Phleum pratense.=
5b. Lower scales unawned; stem branched at the base =Floating Foxtail, Alopecurus geniculatus.=
6a. Bristles 5 or more at the base of each spikelet =Yellow Foxtail, Setaria glauca.=
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 Gra.s.s) --10.
9b. Spikelets with awns; plants 12 dm. high or more --12.
10a. Leaf-sheaths all glabrous. =Crab Gra.s.s, Digitaria humifusa.=
10b. Lower leaf-sheaths hairy --11.
11a. Axis of the spike flat, with wing-like margins =Crab Gra.s.s, Digitaria sanguinalis.=
11b. Axis of the spike slender, without winged margins =Crab Gra.s.s, Digitaria filiformis.=
12a. Spikes numerous, appressed to the axis of the panicle; tall marsh gra.s.s =Slough Gra.s.s, Spartina michauxiana.=
12b. Spikes 2-6, widely divergent; plant of dry ground =Blue-joint, Andropogon furcatus.=
13a. Spikelets subtended by an ovoid th.o.r.n.y involucre 3-8 mm. wide =Sand Bur, Cenchrus carolinia.n.u.s.=
13b. Spikelets without a th.o.r.n.y involucre --14.
14a. Lower branches of the panicle spreading, bearing staminate flowers, the upper branches erect, with pistillate flowers; aquatic or marsh gra.s.s 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 Gra.s.s, Andropogon scoparius.=
16b. Spikelets in branching cl.u.s.ters; 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 coa.r.s.e =Barnyard Gra.s.s, 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-gra.s.s, 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 Gra.s.s, Panic.u.m capillare.=
19b. Panicle of smaller size =Panic-gra.s.ses, various species of Panic.u.m.=
20a. Panicle strongly contracted or spike-like; plants of sand-dunes --4a.
20b. Panicle spreading or slightly contracted; axis of the spikelet beset with bristles; leaves 2 dm. long or more; marsh gra.s.s =Reed Gra.s.s, Calamagrostis canadensis.=
20c. Panicle spreading or somewhat contracted, but not spike-like; axis of the spikelet without bristles --21.
21a. Panicle-branches erect or ascending --22.
21b. Panicle-branches strongly spreading --23.
22a. The two outer scales of the spikelet one-fourth as long as the third scale, or sometimes one of them absent --17a.
22b. The glumes at least half as long as the lemma =Wood-gra.s.s, Muhlenbergia mexicana.=
23a. The chief lateral branches of the panicle dividing and bearing flowers below their middle =Red-top, Agrostis alba.=
23b. The chief branches of the panicle dividing only beyond the middle =Hair Gra.s.s, Agrostis hyemalis.=
24a. Spikelets arranged in two rows to form a definite spike --25.
24b. Spikelets in panicles, never in definite rows --29.
25a. Spikelets in a single row on one side of the axis, forming a one-sided spike =Yard Gra.s.s, Eleusine indica.=
25b. Spikelets alternating on opposite sides of the axis, forming a two-rowed spike --26.
26a. Spikelets in pairs at each joint, forming a dense spike (Wild Rye) --27.
26b. Spikelets single at each joint, forming a loose, open or interrupted spike --28.