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Keyed in multiple places:

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Key to Poaceae, Key L: grasses with 1 floret and awned lemmas

Poaceae

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© Scott Ward
1 Lemma awn 3-branched (the lateral 2 sometimes very reduced compared to the central); [tribe Aristideae]
(c) Fleming, Gary P.
1 Lemma awned with a simple awn.
  2 Upper glumes present, 1-veined; lower glumes absent or much shorter than the upper glumes and veinless; [tribe Brachyelytreae]
  2 Both glumes present, 1-many-veined.
    3 Lemma hardened, distinctly different than the glumes in texture when mature; [tribe Stipeae].
      4 Rhizomatous perennials; primary leaves cauline (the basal leaves < 2 cm long or merely represented by sheaths), 8-16 mm wide
      4 Cespitose perennials; primary leaves basally disposed, 0.2-10 mm wide.
        5 Leaves > 4 mm wide.
          6 Florets 2.5-3.5 mm long; awns 3.4 mm long; [exotic, rarely naturalized]
          6 Florets 5-13 mm long; awns either 7-15 or 30-120 mm long; [exotics or natives].
             7 Leaves 2-8 mm wide, not twisted at the base; awns 30-120 mm long
             7 Leaves 4-10 mm wide, the base twisted so that the abaxial surface is uppermost; awns 7-15 mm long
        5 Leaves < 4 mm wide.
(c) Fleming, Gary P.
               8 Florets 7-25 mm long; awns 30-225 mm long.
                 9 Palea grooved, longer than the lemma; lemma margins involute, fitting into the paleal groove; [native species, collectively widespread in our area]
                 9 Palea flat, shorter than or equal to the lemma; lemma margin convolute or not overlapping; [exotic species, rare in our area]
                   10 Lemma margins not or only slightly overlapping at maturity; awns 60-190 mm long
                   10 Lemma margins strongly overlapping for their entire length at maturity; awns 40-120 mm long
               8 Florets 1.5-4.5 mm long; awns 1-35 mm long
                     11 Leaves 0.2-0.6 mm wide; florets 1.5-2.5 mm long; awns 15-35 mm long
                     11 Leaves 0.5-10 mm wide; florets 2.2-4.5 mm long; awns 1-15 mm long.
                       12 Leaves 0.5-1.8 mm wide; central vein of the lemma not prominent; [native species]
    3 Lemma neither hardened nor distinctly different than the glumes in texture when mature.
                            14 All spikelets sessile or subsessile and arrayed along inflorescence axes (racemes) divergent from the central axis (but not both overlapping one another and clearly ranked on one side of the axis, so as to be keyed under Key H).
                              15 Inflorescences with disarticulating branches; Lower glumes 0.9-4 mm long; spikelets disarticulating below the glumes, the spikelet falling as a whole; spikelets appressed to divergent from the raceme axes; sheaths not strongly overlapping; [tribe Cynodonteae; subtribe Eleusininae]
                              15 Inflorescences without disarticulating branches; lower glumes 1.5-3 mm long (Muhlenbergia paniculata) or (2-) 3.5-7 mm long (Gymnopogon); spikelets disarticulating above the glumes (which often remain on the inflorescence); spikelets strongly appressed to the raceme axes; sheaths strongly overlapping or not , if so then at least on the upper culm, therefore hiding the culm; [tribe Cynodonteae; subtribe “incertae sedis”]
                                16 Blades with thick, white margins and well-developed midrib; inflorescence branches strongly divergent; glumes unequal, usually shorter (sometimes only slightly so) than the solitary floret
                                16 Blades lacking both thick, white margins and well-developed midribs; glumes subequal, usually exceeding the 1-2(4) floret(s)
                            14 Spikelets pedicellate and arrayed in a more complex, open (and sometimes loosely contracted) panicle.
                                    18 Spikelets disarticulated below the glumes, the spikelet falling intact, leaving a naked pedicel; [tribe Poeae]
                                    18 Spikelets disarticulated above the glumes, the floret falling, leaving the glumes attached to the pedicels.
                                         20 Lemmas faintly 5-veined; awn from the back of the lemma; lower glume longer than the lemma; palea much shorter than the lemma (or absent); [tribe Poeae]
                                         20 Lemmas strongly 3-veined; awn from the tip of the lemma; lower glume shorter than (rarely equaling) the lemma; palea about equaling the lemma; [tribe Cynodonteae; subtribe Muhlenbergiinae]
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Key to Poaceae, Key M: grasses with 2+ florets, these exceeded and usually concealed by the glumes

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1 Spikelets disarticulating below the glumes, the spikelets falling as a whole or in clusters; [tribe Poeae]
1 Spikelets disarticulating above the glumes, the glumes remaining attached to the pedicel.
  2 Spikelets dimorphic, paired, each pair consisting of a lower spikelet with sterile florets and an upper spikelet one with fertile florets; [tribe Poeae]
    3 Spikelets each with 1 fertile (bisexual) floret, with 1-several sterile florets, either towards the base or towards the tip of the spikelet.
      4 Fertile floret basal, with 1-several sterile florets towards the tip of the spikelet; [tribe Cynodonteae; subtribe “incertae sedis”]
      4 Fertile floret terminal, with 1-several sterile florets towards the base of the spikelet (the sterile florets sometimes knoblike or like tufts of hairs, and not obviously like florets); [tribe Poeae].
        5 Spikelets with 2 florets, the lower floret staminate and of similar size as the upper, pistillate or bisexual floret; lemma of the lower floret awned; lemma of the upper floret unawned or awned
        5 Spikelets with 2-3 florets, the lower 1-2 florets staminate or sterile, either highly reduced to knobs or tufts of hairs, or shorter than to longer than the terminal, bisexual floret; lemma of the lower florets either awned or unawned; lemma of the upper floret unawned.
          6 Lower sterile florets 2, shorter than to exceeding the bisexual floret; fresh leaves with sweet vanilla odor when crushed; lemma of the lower florets awned or unawned
             7 Glumes unequal, the lower shorter than the upper; lowest 2 florets sterile.
          6 Lower sterile florets 1-2, either highly reduced to knobs or tufts of hairs, or consisting of linear to lanceolate lemmas up to ¾ as long as the bisexual floret; all lemmas unawned
    3 Spikelets each with 2 or more fertile florets.
               8 Spikelets 18-50 mm long; glumes 9-11-veined; [tribe Poeae]
               8 Spikelets 2.5-20 mm long; glumes 1-7-veined.
                 9 Lemma awns apical or dorsal (arising from the apex or back of the lemma or sometimes the midvein prolonged into a 1 mm awn), or sometimes awns absent (Rostraria).
                   10 Spikelets 7-20 mm long, with 3-12 florets; ligule of hairs; lemma awn 5-15 mm long; [collectively widespread in our area]; [tribe Danthoniae]
                   10 Spikelets 2.5-7.5 mm long, with 2-3(-6) florets; ligule membranous, sometimes ciliolate (only ciliolate in Rostraria) but otherwise not only consisting of hairs, 0.5-4 mm long; lemma awn 1-9 mm long; [tribe Poeae].
                       12 Awns of the lemmas 1 mm long, essentially a minute prolonged extension of the lemma midvein; lemma apices acute
                       12 Awns of the lemmas 2-8 mm long, therefore conspicuous and not merely a minute midvein extension, bent or geniculate and often basally-twisted and exceeding lemma apices; lemma apices bifid or bicuspidate.
                          13 Panicle branches densely pubescent, usually glistening yellowish-brown or yellowish to tan; panicles either 1-5 cm (Trisetum aureum) OR 5-20 cm long (Trisetum flavescens); leaves evenly distributed; ligules 0.5-1(2) mm, obtuse, lacerate, sometimes ciliolate; plants sometimes with rhizomes to 7 cm long (T. flavescens); [occurring very sporadically in disturbed sites throughout our area or as a ballast waif in NJ]
                          13 Panicles branches glabrous or sparsely pubescent, usually silvery-shiny; panicles (5)20-30(50) cm long; leaves mostly basal or evenly distributed; ligules 0.5-4 mm, truncate or rounded; plants not rhizomatous; [a native of cool, moist, undisturbed northern sites; rare and disjunct in high elevation areas s. to VA]
                 9 Lemma awns basal (arising from the lower half of the lemma); [tribe Poeae].
                            14 Awns geniculate and articulated near the middle joint with a ring of minute conical protuberances, the distal segment of the lemma clavate and differing in shape from the proximal lemma segment; [NJ and PA northward]
                            14 Awns straight or geniculate (sometimes only slightly so), if geniculate then the awn not bearing a distinct ring at the joint and not bearing a clavate distal segment; [collectively widespread].
                                16 Lemma awn 4-8 mm long, geniculate, exserted beyond the tips of the glumes; lemmas minutely scabrous, dull; leaf blades involute, appearing filiform (rounded in cross-section); ligule 0.5-3 (-5) mm long
                                16 Lemma awn 2-3 mm long, straight or nearly so, scarcely (or not at all) exserted beyond the tips of the glumes; lemmas smooth, shiny; leaf blades flat or folded at the midvein (V-shaped in cross-section); ligule 3-10 (-17) mm long