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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
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