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Keyed in multiple places:

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Key to Poaceae, Key B: robust herbaceous grasses

Poaceae

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1 Inflorescence an array of spikes, the spikelets closely imbricate in 2 rows along the rachis of the spikes, the spikes alternate along the primary inflorescence axis; [tribe Zoysieae; subtribe Sporobolinae]
1 Inflorescence otherwise, either the spikelets embedded or in grooves in an thickened rachis, or the inflorescence a slender or broad panicle.
  2 Spikelets embedded in the thickened rachis (the inflorescence thus like an ear of corn), or fitting into grooves in the thickened rachis (the inflorescence thus cylindrical and resembling a rat's tail). Spikelets unisexual, with male and female spikelets in separate inflorescences or in different parts of the same inflorescence; [tribe Andropogoneae].
    3 Racemes of mixed sex (female below, male above)
    3 Racemes of single sex
 Zea
  2 Spikelets not embedded or fitting into grooves in the rachis, the inflorescence a slender or broad panicle (the spikelets visibly separate and often pedicelled).
      4 Spikelets with a single floret, this unisexual (either pistillate or staminate); plants with aerenchymatous culms, [plants of seasonally or tidally flooded wetlands]; [tribe Oryzeae].
        5 Pistillate spikelets on the upper branches of the panicle, staminate spikelets on the lower branches; lemmas and paleas clasping along their margins; plants annual
        5 Pistillate and staminate spikelets intermingled on the same branches of the inflorescence; lemma margins free; plants perennial
      4 Spikelets with 2 or more florets, at least some of these bisexual; plants without aerenchymatous culms, [plants of uplands or temporarily to seasonally flooded wetlands].
             7 Leaves primarily basal, plants densely cespitose.
             7 Leaves cauline; plants short to long rhizomatous, usually somewhat clumped (short rhizomatous to cespitose in Neyraudia).
                 9 Lemmas 3-veined, the apices bifid and shortly awned from between the teeth; [tribe Cynodonteae]
                 9 Lemmas 3-7 veined, the apices not bifid (instead either unawned, entire, or only minutely awned); plants rhizomatous; [tribe Arundineae]
                   10 Lemmas pilose; rachilla glabrous; plants short-rhizomatous (somewhat clumped); culms to 10 m tall; [plants of uplands or saturated or temporarily flooded wetlands]
                   10 Lemmas glabrous; rachilla sericeous; plants long rhizomatous; culms to 4 m tall; [plants of uplands or saturated, tidally flooded, or seasonally flooded wetlands]
          6 Spikelets almost always with 2 florets, the lower florets sterile or staminate (sometimes reduced to lemmas or completely absent).
                     11 Spikelets falling separately, not attached to rachis segments, stalks, or bristles; spikelets <2× as long as wide; [tribe Paniceae].
                       12 Spikelets (at least the terminal) subtended by 1-many stiff, terete bristles
                            14 Fertile (upper) florets shiny and black to brown-colored when mature; the glumes abruptly apiculate and (internally) oily, the lower glume bases saccate; plants erect, arching, climbing, or decumbent; [s. FL only in our flora area]
                            14 Fertile florets not shiny and black when mature; glume apices truncate to acuminate, but not abruptly apiculate (nor internally oily); plants growing variously, but rarely arching or decumbent
                     11 Spikelets falling with attached rachis segments, stalks, or bristles; spikelets >3× as long as wide; [tribe Andropogoneae].
                              15 Pedicelled spikelet differing from the sessile in shape and sex (sometimes represented only by a pedicel).
                                       19 Spikelets awned with awns 10-26 mm long; anthers 2; [native, collectively common and widespread]

Key to Poaceae, Key D: rattail or cob grasses

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1 All spikelets unisexual, the pistillate and staminate spikelets either in separate inflorescences, or the pistillate spikelets below the staminate spikelets in the same inflorescence; leaves 9-120 mm wide; [tribe Andropogoneae].
1 Some spikelets bisexual; leaves 1-25 mm wide.
    3 Spikelets with 2-7 florets, the lower bisexual and fertile, the upper sometimes sterile; [tribe Triticeae]
    3 Spikelets with at most 2 florets, the lower staminate or sterile, the upper bisexual, staminate, or sterile.
      4 Culms 2-45 cm tall; leaves 1-6 mm wide; plants annual (perennial in Eremochloa and Stenotaphrum).
        5 Plants obviously and prominently rhizomatous (Eremochloa) or stoloniferous (Stenotaphrum); lower glume with pectinate margins (Eremochloa) or irregularly toothed (Stenotaphrum)
          6 Plant rhizomatous; lower glume with pectinate margins; [commonly naturalized turf grass and roadside weed]; [tribe Andropogoneae]
          6 Plant stoloniferous; lower glume irregularly toothed; [naturalized turf grass and allegedly also native]; [tribe Paniceae]
        5 Plants annual; lower glume with smooth and cartilaginous margins (or absent); [rare waifs]; [tribe Poeae].
      4 Culms 30-400 cm tall; leaves 2-25 mm wide; plants annual or perennial; [tribe Andropogoneae].
                 9 Pedicels at least partially fused to the rame axes
                   10 Sheaths mostly glabrous (sparsely ciliate towards the base); plants perennial
                   10 Sheaths with stiff, papillose-based hairs 1-3 mm long; plants annual

Key to Poaceae, Key E: grasses of tribe Andropogoneae (also including grasses also keyed in Keys B, C, and D)

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1 Leaves ovate-lanceolate, 2-10 cm long, 2.5-7× as long as wide; plants weak-stemmed annuals, branching, decumbent, rooting at the lower nodes; [exotic weeds].
  2 Leaves cordate-clasping at base; spikelets awned, not paired, unaccompanied by a vestige; each panicle with 12-20 rames
  2 Leaves tapering to a broadly cuneate base; spikelets unawned, paired (one of the pair sometimes vestigial); each panicle with 1-few rames
1 Leaves lanceolate to linear, either longer or proportionately narrower; plants either perennial or coarse annuals with erect and mostly unbranched culms.
    3 Spikelets embedded in the thickened rachis (the inflorescence thus like an ear of corn), or fitting into grooves in the thickened rachis (the inflorescence thus cylindrical and resembling a rat's tail), or the pistillate inflorescences enclosed in a hard, bead-like, pearly-white, modified bract.
      4 Spikelets unisexual, with male and female spikelets in separate inflorescences or in different parts of the same inflorescence.
        5 Internode narrower than and more-or-less enclosed by the female spikelet
        5 Internode broader than and more-or-less enclosing the female spikelet.
          6 Racemes of mixed sex, female flowers below, and male above
          6 Racemes of single sex, the female inflorescences (“ears”) borne on axillary branches, the male inflorescences (“tassels”) terminal on the culm
 Zea
      4 Spikelets, or at least one of each pair, bisexual.
             7 Culms 2-45 cm tall; leaves 1-5 mm wide; plants perennial, obviously and prominently rhizomatous; lower glume with pectinate margins; [commonly naturalized turf grass and roadside weed]
             7 Culms 30-400 cm tall; leaves 2-25 mm wide; plants annual or perennial, cespitose or short-rhizomatous; lower glume winged or not, but not pectinate.
    3 Spikelets not embedded or fitting into grooves in the rachis, the rachis slender (the spikelets visibly separate and often pedicelled).
                       12 Spikelets falling in pairs together with sections of the disarticulating rachis.
                            14 Spikelets awned with awns 10-26 mm long; anthers 2; [native, collectively common and widespread]
                            14 Spikelets unawned or with awns to 5.2 mm long; anthers 3; [exotic, rarely encountered]
                     11 Pedicelled spikelet differing from the sessile in shape and sex (sometimes represented only by a pedicel).
                                       19 Inflorescence a false panicle with numerous inflorescence units; peduncles with 2 rames in digitate clusters (1 almost sessile, the other rame stalked and both bearing 7-14 heterogamous spikelet pairs), disarticulation in the rames beneath the bisexual spikelets; spikelets a mix of heterogamous and homogamous pairs; awns of the lemma 1-3.5 cm long; [non-natives]
                                       19 Inflorescences true panicles (with evident rachises); disarticulation beneath the sessile spikelets (or not occurring at all); spikelets only heterogamous; awns of the lemma (5-) 10-40 mm long (when present); [native and non-natives].
                                             22 Pedicels of the pedicelled (reduced or absent) spikelets strongly flattened and with or without grooves on both sides.