1	"Lemmas strongly keeled, at least distally; spikelets strongly laterally compressed; lower glumes 3–7(9)-veined"	2
1	"Lemmas rounded over the midvein; spikelets terete to moderately laterally compressed; lower glumes 1–5-veined"	9
2	"Lemmas unawned or with awns to 3.5 mm long; lemmas usually glabrous, sometimes pubescent distally, veins prominent for most of their length"	"Bromus catharticus"
2	"Lemmas awned, awns (2)4–17 mm long; lemmas pubescent or glabrous, veins obscure or prominent"	3
3	"Lower panicle branches shorter than 20 cm, with 1–3 spikelets on the distal 1/2, sometimes confined to the tips; culms 3–7 mm thick"	4
3	"Lower panicle branches usually less than 10 cm long, with 1–5 spikelets variously distributed; culms less than 4 mm thick"	5
4	"Lower panicle branches shorter than 20 cm, spreading to drooping"	"Bromus sitchensis"
4	"Lower panicle branches shorter than 10 cm, stiffly ascending"	"Bromus aleutensis"
5	"Upper glume about as long as the lowest lemma in each spikelet; lemmas glabrous or pubescent distally or throughout, the marginal hairs, if present, longer than those elsewhere"	"Bromus arizonicus"
5	"Upper glume shorter than the lowest lemma in each spikelet; lemmas glabrous or pubescent only on the margins or throughout, if throughout, the marginal hairs similar in length to those elsewhere"	6
6	"Panicles dense; spikelets crowded, overlapping, usually longer than the pedicels and branches; culms 20–70 cm tall, sometimes geniculate at the base; blades glabrous, smooth or scabrous; ligules 1–6 mm long"	"Bromus maritimus"
6	"Panicles loose to compact; spikelets not crowded or overlapping, shorter than at least some pedicels and branches; culms 30–120(180) cm tall, erect or decumbent; blades glabrous or hairy; ligules 1–4 mm long"	7
7	"Lemmas and sheath throats glabrous"	"Bromus polyanthus"
7	"Lemmas and/or sheath throats with hairs"	8
8	"Lemmas 9–13-veined, veins often raised and riblike distally or throughout"	"Bromus catharticus"
8	"Lemmas 7–9-veined, veins usually not raised or riblike"	"Bromus carinatus"
9	"Awns, if present, arising less than 1.5 mm below the lemma apices; lemma apices entire, emarginate, or with teeth less than 1 mm long"	10
9	"Awns arising 1.5 mm or more below the lemma apices, lemma apices entire, emarginate, or with teeth to 5 mm long"	59
10	"Lower glumes 1–3-veined; upper glumes 3–5-veined; plants perennial or annual, if annual, the lower glumes 1-veined and the upper glumes 3-veined"	11
10	"Lower glumes 3–5-veined; upper glumes 5–9-veined; plants annual or biennial, if biennial, the upper glumes 7-veined and/or the lateral veins of the lemmas prominently ribbed"	42
11	"Plants rhizomatous"	12
11	"Plants not rhizomatous"	14
12	"Culms 30–90 cm long, forming distinct clumps; rhizomes short"	"Bromus riparius"
12	"Culms 50–135 cm long, single or few together; rhizomes short to long-creeping"	13
13	"Lemma backs sparsely to densely hairy throughout, or on the lower portion and margins, or along the marginal veins and keel; cauline nodes and leaf blades pubescent or glabrous; awns usually present, to 7.5 mm long, sometimes absent"	"Bromus pumpellianus"
13	"Lemma backs usually glabrous, occasionally sparsely puberulent at the base and sometimes on the margins; cauline nodes and leaf blades usually glabrous, rarely hairy; awns absent or to 3 mm long"	"Bromus inermis"
14	"Anthers (3.5)4–6(6.8) mm long; awns 2.5–7.5 mm long; plants of the Yukon River drainage of Alaska"	"Bromus pumpellianus"
14	"Anthers 1–7 mm long; awns 1–12 mm long; plants of various locations in the Flora region, if in the Yukon River drainage of Alaska, anthers 1–1.4 mm long"	15
15	"Culms with 9–20 nodes; collars and throats densely pilose; auricles 1–2.5 mm long on most lower leaves"	"Bromus latiglumis"
15	"Culms with (1)2–9 nodes; collars and throats pubescent or glabrous; auricles, if present, of various lengths"	16
16	"Most lower glumes within a panicle 3-veined, sometimes some 1-veined"	17
16	"Most lower glumes within a panicle 1-veined, sometimes some 3-veined"	26
17	"Most upper glumes within a panicle 5-veined, sometimes some 3-veined"	18
17	"Most upper glumes within a panicle 3-veined, sometimes some 5-veined"	21
18	"Awns 1.5–3 mm long; anthers 1.5–2.5 mm long; ligules 0.5–1 mm long"	"Bromus kalmii"
18	"Awns 3–7 mm long; anthers 3–6 mm long; ligules to 4.2 mm long"	19
19	"Glumes glabrous, sometimes scabrous; ligules glabrous"	"Bromus laevipes"
19	"Glumes usually pubescent, rarely glabrous, sometimes scabrous; ligules usually pubescent or pilose, sometimes glabrous"	20
20	"Margins of the glumes and lemmas often bronze-tinged; ligules to 1.5 mm long; auricles usually present on the lower leaves, rarely absent"	"Bromus pseudolaevipes"
20	"Margins of the glumes and lemmas not bronze-tinged; ligules 1–3 mm long; auricles sometimes present"	"Bromus grandis"
21	"Culms 70–180 cm tall; awns 3–8 mm long; anthers 3–6 mm long"	22
21	"Culms 30–100 cm tall; awns 1–4 mm long; anthers (1)1.5–4 mm long"	24
22	"Lower leaf sheaths pilose, with hairs 2–4 mm long; blades glabrous or with pilose edges"	"Bromus orcuttianus"
22	"Lower leaf sheaths densely pubescent, with hairs to 1 mm long; blades densely pubescent"	23
23	"Leaf blades 7.5–16.5 cm long; culm nodes 1–2(3)"	"Bromus hallii"
23	"Leaf blades (13)18–38 cm long; culm nodes 3–7"	"Bromus grandis"
24	"Leaf blades often glaucous; glumes usually glabrous, rarely slightly pubescent"	"Bromus frondosus"
24	"Leaf blades not glaucous; glumes usually pubescent, rarely glabrous"	25
25	"Midrib of the culm leaves abruptly narrowed just below the collar; auricles frequently present on the lower leaves; plants of western Texas"	"Bromus anomalus"
25	"Midrib of the culm leaves not abruptly narrowed just below the collar; auricles absent; plants of western North America, including Texas"	"Bromus porteri"
26	"Upper glumes within a panicle consistently 5-veined; collars with a dense line of hairs; lower sheaths often sericeous; ligules 0.4–1 mm long"	"Bromus nottowayanus"
26	"All or most upper glumes within a panicle 3-veined, sometimes some with 2 additional faint lateral veins; collars glabrous or hairy, hairs evenly distributed over the surface, not in a dense line; lower sheaths glabrous or hairy, not sericeous; ligules to 6 mm long"	27
27	"Plants annual; lemmas glabrous, sometimes scabrous; ligules pubescent"	"Bromus texensis"
27	"Plants perennial; lemmas usually pubescent on the backs and/or margins, sometimes glabrous or scabrous; ligules usually glabrous, sometimes pubescent or pilose"	28
28	"Awns (4)6–12 mm long; ligules 2–6 mm long"	"Bromus vulgaris"
28	"Awns 1–8 mm long; ligules to 4 mm long"	29
29	"Blades densely pubescent on both surfaces, 7.5–16.5 cm long; anthers 3–6 mm long; awns 3.5–7 mm long"	"Bromus hallii"
29	"Blades glabrous or hairy on 1 or both surfaces, (3)5–60 cm long, if 7.5–16.5 cm long and densely pubescent on both surfaces, then anthers 1–4 mm long and/or awns 1–4 mm long"	30
30	"Panicle branches appressed to slightly spreading; culm nodes 1–4"	31
30	"Panicle branches ascending to drooping; culm nodes (1)2–8"	33
31	"Awns 2–5 mm long; anthers 2–3.5 mm long; blades flat"	"Bromus suksdorfii"
31	"Awns (4)5–8 mm long; anthers 3–6.5 mm long; blades sometimes involute"	32
32	"Culms 90–150 cm long; ligules 1–3 mm long"	"Bromus orcuttianus"
32	"Culms 50–100 cm long; ligules to 1.5 mm long"	"Bromus erectus"
33	"Midrib of the culm leaves abruptly narrowed just below the collar; auricles frequently present on the lower leaves; plants of western Texas"	"Bromus anomalus"
33	"Midrib of the culm leaves not abruptly narrowed just below the collar; auricles sometimes present; plants of various distribution, including Texas"	34
34	"Glumes usually pubescent, rarely glabrous"	35
34	"Glumes usually glabrous, sometimes pubescent"	39
35	"Upper glume mucronate"	"Bromus mucroglumis"
35	"Upper glume not mucronate"	36
36	"Awns (1)2–3(3.5) mm long; blades 2–6 mm wide"	"Bromus porteri"
36	"Awns 3–7(8) mm long; blades 3–19 mm wide"	37
37	"Anthers 3–6 mm long; ligules densely pubescent to pilose"	"Bromus grandis"
37	"Anthers 2–4(5) mm long; ligules glabrous"	38
38	"Ligules 2–4 mm long"	"Bromus pacificus"
38	"Ligules 0.5–2 mm long"	"Bromus pubescens"
39	"Ligules 2–3.5 mm long; auricles present"	"Bromus ramosus"
39	"Ligules 0.4–2 mm long; auricles sometimes present"	40
40	"Lemma margins and backs usually pubescent, sometimes nearly glabrous; awns 2–4 mm long; anthers 1.8–4 mm long"	"Bromus lanatipes"
40	"Lemma margins conspicuously hirsute or densely pilose, at least along the lower 1/2, the backs glabrous at least on the lower lemmas in a spikelet; awns 3–5 mm long; anthers 1–2.7 mm long"	41
41	"Backs of all lemmas glabrous; anthers 1–1.4 mm long; upper glumes 7.1–8.5 mm long"	"Bromus ciliatus"
41	"Backs of the upper lemmas in a spikelet hairy; anthers 1.6–2.7 mm long; upper glumes 8.9–11.3 mm long"	"Bromus richardsonii"
42	"Lemmas inflated, 6–8 mm wide; unawned or with awns up to 1 mm long; spikelets ovate"	"Bromus briziformis"
42	"Lemmas not inflated, 1–7 mm wide; awns 2–25 mm long, rarely lacking; spikelet shape various"	43
43	"Lemma margins inrolled at maturity; floret bases visible at maturity; rachilla internodes visible at maturity; caryopses sometimes thick, strongly inrolled"	44
43	"Lemma margins not inrolled at maturity; floret bases concealed at maturity; rachilla internodes concealed at maturity; caryopses thin, weakly inrolled or flat"	46
44	"Anthers 2.5–5 mm long; awns straight; spikelets often purple-tinged; lower leaf sheaths softly appressed-hairy"	"Bromus arvensis"
44	"Anthers 0.7–2 mm long; awns straight or flexuous; spikelets not purple-tinged; lower leaf sheaths glabrous, loosely pubescent and glabrate, or evenly covered with stiff hairs"	45
45	"Lower leaf sheaths glabrous or loosely pubescent and glabrate; lemmas 6.5–8.5(10) mm long, margins evenly rounded; awns straight or flexuous"	"Bromus secalinus"
45	"Lower leaf sheaths evenly covered with stiff hairs; lemmas 8–11.5 mm long, margins bluntly angled; awns straight"	"Bromus commutatus"
46	"Lemmas 4.5–6.5 mm long, margins sharply angled; caryopses longer than the paleas"	"Bromus lepidus"
46	"Lemmas 6.5–20 mm long, margins rounded or slightly to strongly angled; caryopses equaling or shorter than the paleas"	47
47	"Awns arising less than 1.5 mm below the lemma apices, erect or weakly divaricate, not twisted at the base"	48
47	"Awns arising 1.5 mm or more below the lemma apices, erect to strongly divaricate, often twisted at the base"	51
48	"Panicle branches shorter than the spikelets; lemmas chartaceous, with prominent ribs over the veins, often concave between the veins; anthers 0.6–1.5 mm long"	"Bromus hordeaceus"
48	"At least some panicle branches longer than the spikelets; lemmas coriaceous, veins obscure or distinct, not ribbed; anthers 0.7–5 mm long"	49
49	"Lower leaf sheaths softly appressed-hairy; anthers 2.5–5 mm long; panicles 11–30 cm long"	"Bromus arvensis"
49	"Lower leaf sheaths with stiff hairs; anthers 0.7–3 mm long; panicles 4–16 cm long"	50
50	"Anthers 0.7–1.7 mm long; rachilla internodes 1.5–2 mm long; lemmas 8–11.5 mm long, margins bluntly angled"	"Bromus commutatus"
50	"Anthers 1.5–3 mm long; rachilla internodes 1–1.5 mm long; lemmas 6.5–8 mm long, margins rounded"	"Bromus racemosus"
51	"Panicle branches shorter than the spikelets, slightly curved or straight, panicles erect."	52
51	"At least some panicle branches as long as or longer than the spikelets, sometimes sinuous; panicles nodding"	56
52	"At least the upper lemmas in each spikelet with 3 awns"	"Bromus danthoniae"
52	"All lemmas 1-awned"	53
53	"Lemmas 11–20 mm long; spikelets 20–50 mm long"	54
53	"Lemmas 6.5–11 mm long; spikelets 11–25 mm long"	55
54	"Spikelets usually single at the nodes; glumes glabrous or puberulent; panicles strongly contracted, even at maturity"	"Bromus caroli-henrici"
54	"Spikelets often 2 or more at each node; glumes pilose; panicles contracted when immature, more open with age"	"Bromus lanceolatus"
55	"Lemmas 1.5–2 mm wide; panicles obovoid, branches sometimes verticillate"	"Bromus scoparius"
55	"Lemmas 3–5 mm wide; panicles usually ovoid"	"Bromus hordeaceus"
56	"Lower glumes 7–10 mm long; upper glumes 8–12 mm long; panicle branches conspicuously sinuous; awns erect to weakly spreading; lemma margins rounded"	"Bromus arenarius"
56	"Lower glumes 4–7 mm long; upper glumes 5–8 mm long; panicle branches sometimes sinuous; awns erect to strongly divergent; lemma margins slightly to strongly angled above the middle"	57
57	"Anthers 2.5–5 mm long; spikelets often purple-tinged; culms 80–110 cm tall"	"Bromus arvensis"
57	"Anthers 1–1.5 mm long; spikelets not purple-tinged; culms 20–70 cm tall"	58
58	"Lemmas with hyaline margins 0.3–0.6 mm wide, slightly angled above the middle; branches somewhat drooping, sometimes sinuous, often with more than 1 spikelet"	"Bromus japonicus"
58	"Lemmas with hyaline margins 0.6–0.9 mm wide, strongly angled above the middle; branches not drooping or sinuous, usually with 1 spikelet"	"Bromus squarrosus"
59	"Awns usually geniculate, sometimes only divaricate, lemma teeth 2–3 mm long, usually aristate, sometimes only acuminate"	"Bromus berteroanus"
59	"Awns straight, arcuate, or divaricate, not geniculate, sometimes absent; lemma teeth absent or to 5 mm long, acuminate"	60
60	"Lower glumes 1–3-veined; upper glumes 3–5-veined; spikelets with parallel or diverging sides in outline, often widening distally; lemma apices bifid, teeth (0.8)1–5 mm long"	61
60	"Lower glumes 3–5-veined; upper glumes 5–9-veined; spikelets with parallel or converging sides in outline; lemma apices entire to bifid, teeth less than 1 mm long, sometimes split and appearing longer"	65
61	"Lemmas 20–35 mm long"	"Bromus diandrus"
61	"Lemmas 9–20 mm long"	62
62	"Spikelets usually shorter than the panicle branches; panicle branches ascending to spreading or drooping"	63
62	"Spikelets longer than the panicle branches; panicle branches ascending to spreading, never drooping"	64
63	"Lemmas 14–20 mm long; panicles with spreading, ascending, or drooping branches, rarely with any branches with more than 3 spikelets"	"Bromus sterilis"
63	"Lemmas 9–12 mm long; panicles with drooping branches, often with 1 or more branches with 4–8 spikelets"	"Bromus tectorum"
64	"Some panicle branches 1–3+ cm long, most branches visible"	"Bromus madritensis"
64	"Panicle branches 0.1–1 cm long, usually not readily visible"	"Bromus rubens"
65	"Lemmas inflated, 6–8 mm wide; unawned or with awns up to 1 mm long; spikelets ovate"	"Bromus briziformis"
65	"Lemmas not inflated, 1–7 mm wide; awns 2–25 mm long, rarely lacking; spikelet shape various"	66
66	"Lemma margins inrolled at maturity; floret bases visible at maturity; rachilla internodes visible at maturity; caryopses sometimes thick, strongly inrolled"	67
66	"Lemma margins not inrolled at maturity; floret bases concealed at maturity; rachilla internodes concealed at maturity; caryopses thin, weakly inrolled or flat"	69
67	"Anthers 2.5–5 mm long; awns straight; spikelets often purple-tinged; lower leaf sheaths softly appressed-hairy"	"Bromus arvensis"
67	"Anthers 0.7–2 mm long; awns straight or flexuous; spikelets not purple-tinged; lower leaf sheaths glabrous, loosely pubescent and glabrate, or evenly covered with stiff hairs"	68
68	"Lower leaf sheaths glabrous or loosely pubescent and glabrate; lemmas 6.5–8.5(10) mm long, margins evenly rounded; awns straight or flexuous"	"Bromus secalinus"
68	"Lower leaf sheaths evenly covered with stiff hairs; lemmas 8–11.5 mm long, margins bluntly angled; awns straight"	"Bromus commutatus"
69	"Lemmas 4.5–6.5 mm long, margins sharply angled; caryopses longer than the paleas"	"Bromus lepidus"
69	"Lemmas 6.5–20 mm long, margins rounded or slightly to strongly angled; caryopses equaling or shorter than the paleas"	70
70	"Awns arising less than 1.5 mm below the lemma apices, erect or weakly divaricate, not twisted at the base"	71
70	"Awns arising 1.5 mm or more below the lemma apices, erect to strongly divaricate, often twisted at the base"	74
71	"Panicle branches shorter than the spikelets; lemmas chartaceous, with prominent ribs over the veins, often concave between the veins; anthers 0.6–1.5 mm long"	"Bromus hordeaceus"
71	"At least some panicle branches longer than the spikelets; lemmas coriaceous, veins obscure or distinct, not ribbed; anthers 0.7–5 mm long"	72
72	"Lower leaf sheaths softly appressed-hairy; anthers 2.5–5 mm long; panicles 11–30 cm long"	"Bromus arvensis"
72	"Lower leaf sheaths with stiff hairs; anthers 0.7–3 mm long; panicles 4–16 cm long"	73
73	"Anthers 0.7–1.7 mm long; rachilla internodes 1.5–2 mm long; lemmas 8–11.5 mm long, margins bluntly angled"	"Bromus commutatus"
73	"Anthers 1.5–3 mm long; rachilla internodes 1–1.5 mm long; lemmas 6.5–8 mm long, margins rounded"	"Bromus racemosus"
74	"Panicle branches shorter than the spikelets, slightly curved or straight, panicles erect."	75
74	"At least some panicle branches as long as or longer than the spikelets, sometimes sinuous; panicles nodding"	79
75	"At least the upper lemmas in each spikelet with 3 awns"	"Bromus danthoniae"
75	"All lemmas 1-awned"	76
76	"Lemmas 11–20 mm long; spikelets 20–50 mm long"	77
76	"Lemmas 6.5–11 mm long; spikelets 11–25 mm long"	78
77	"Spikelets usually single at the nodes; glumes glabrous or puberulent; panicles strongly contracted, even at maturity"	"Bromus caroli-henrici"
77	"Spikelets often 2 or more at each node; glumes pilose; panicles contracted when immature, more open with age"	"Bromus lanceolatus"
78	"Lemmas 1.5–2 mm wide; panicles obovoid, branches sometimes verticillate"	"Bromus scoparius"
78	"Lemmas 3–5 mm wide; panicles usually ovoid"	"Bromus hordeaceus"
79	"Lower glumes 7–10 mm long; upper glumes 8–12 mm long; panicle branches conspicuously sinuous; awns erect to weakly spreading; lemma margins rounded"	"Bromus arenarius"
79	"Lower glumes 4–7 mm long; upper glumes 5–8 mm long; panicle branches sometimes sinuous; awns erect to strongly divergent; lemma margins slightly to strongly angled above the middle"	80
80	"Anthers 2.5–5 mm long; spikelets often purple-tinged; culms 80–110 cm tall"	"Bromus arvensis"
80	"Anthers 1–1.5 mm long; spikelets not purple-tinged; culms 20–70 cm tall"	81
81	"Lemmas with hyaline margins 0.3–0.6 mm wide, slightly angled above the middle; branches somewhat drooping, sometimes sinuous, often with more than 1 spikelet"	"Bromus japonicus"
81	"Lemmas with hyaline margins 0.6–0.9 mm wide, strongly angled above the middle; branches not drooping or sinuous, usually with 1 spikelet"	"Bromus squarrosus"