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Key to Bromus

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1 Lemmas compressed and strongly keeled (the whole spikelet thus strongly laterally flattened); first glume 3-9-nerved; [section Ceratochloa]
1 Lemmas rounded or weakly keeled (the whole spikelet therefore terete to somewhat laterally flattened); first glume either 3-5-nerved or 1-3-nerved.
  2 First glume 3-5 nerved (at least 3 nerves well-developed).
    3 Lemma awn 2-3 mm long; plant perennial; [native species of dry woodlands]; [section Bromopsis]
    3 Lemma awn 3-12 mm long (or 0-6 mm long in B. secalinus); plant annual; [introduced species of disturbed habitats]; [section Bromus].
      4 Panicle compact, the lateral branches erect or ascending, the pedicels < 10 mm long (shorter than the spikelets)
        5 Lemmas 3-5 mm wide; inflorescence ovoid in outline
        5 Lemmas 1.5-2 mm wide; inflorescence obovoid in outline
      4 Panicle relatively open, the lateral branches erect, ascending, or spreading, the pedicels > 15 mm long (longer than the spikelets).
          6 Margins of the lemmas involute in fruit, wrapping around the grain, exposing the rachilla
             7 Spikelets often purple-tinged; lower leaf sheaths bearing soft, appressed hairs; lemma awns 6-11 mm long
             7 Spikelets not purple-tinged; lower leaf sheaths glabrous, loosely pubescent and glabrate, or evenly pilose; lemma awns 0-6 mm (sometimes awns absent or rudimentary)
          6 Margins of the lemmas gaping, overlapping in fruit.
               8 Panicle branches erect or ascending, relatively stiff and straight
               8 Panicle branches spreading (at least the lower), either relatively stiff and straight, or flexuous and lax.
                 9 Panicle branches stiff; lemma awns 5-12 mm long, straight
                 9 Panicle branches flexuous and lax; lemma awns 7-15 mm long, flexuous
  2 First glume 1 (-3) nerved (only 1 nerve well-developed).
                   10 Longer lemma awns 10-60 mm long; plants annual; [introduced species of disturbed habitats]; [section Genea].
                     11 Panicle dense, spikelike
                     11 Panicle open, not spikelike.
                       12 First glume 13-20 mm long; second glume 20-30 mm long; lemma awns 35-60 mm long
                       12 First glume 5-14 mm long; second glume 8-17 mm long; lemma awns 10-30 mm long.
                          13 First glume 7-14 mm long; second glume 9-17 mm long; lemma awns 18-30 mm long
                          13 First glume 5-7 mm long; second glume 8-11 mm long; lemma awn (7-) 10-17 mm long
                   10 Longer lemma awns 1-6 (-8) mm long; plants perennial; [native and introduced species, collectively of disturbed and natural habitats]; [section Bromopsis].
                            14 Plants with creeping rhizomes, forming clonal colonies; both surfaces of leaves glabrous or glabrescent
                            14 Plants not strongly rhizomatous, the stems solitary or tufted; surfaces of leaf blades usually pubescent (sometimes sparsely so).
                              15 Pedicels erect or ascending, mostly shorter than the spikelet; leaves 2-3 mm wide; [introduced, of disturbed habitats]
                              15 Pedicels ascending at first, later arching-drooping, mostly longer than the spikelet; leaves 4-15 mm wide; [mostly native, mostly of forests].
                                16 Lemmas glabrous (or very minutely pubescent) on the back, hairy along the lower margins with long hairs
                                16 Lemmas either uniformly hairy over the entire back-surface (or rarely entirely glabrous), or hairy across at least the lower half of the back-surface.
                                  17 Culms with 2-4 leaves; glumes usually glabrous (scabridulous on the veins); [rare waif, if indeed in our region]
                                  17 Culms with 6-20 leaves; glumes pubescent (sometimes glabrous in some species); [natives, collectively widespread]
                                    18 Culms with 10-20 leaves, often weak and leaning or reclining; junction of sheaths and base of leaf blades with 2 well-developed flanges prolonged into auricles or divergent spurs; second glume primarily 5-nerved; flowering late, with anthesis Aug-Oct
                                    18 Culms with 6-10 leaves, erect; junction of sheaths and base of leaf blades lacking flanges or auricles; second glume primarily 3-nerved; flowering earlier, anthesis from May-Aug.
                                       19 Lower surface of leaf with a conspicuous satiny sheen (when fresh); summit of sheath opposite the ligule with a conspicuous tuft of hairs
                                       19 Lower surface of leaf lacking a conspicuous satiny sheen; summit of sheath opposite the ligule lacking a conspicuous tuft of hairs