1	"Lower glumes 3-7-veined"	2
1	"Lower glumes 1-2(-3) veined"	4
2	"Awns nearly equal, the lateral awns 8-66 mm long and at least 3/4 as long as the central awn"	"Aristida oligantha"
2	"Awns markedly unequal, the lateral awns 1-4 mm long, no more than 1/2 as long as the central awn, sometimes essentially absent"	3
3	"Plants annual; synflorescences 5-12 cm long, 2-4 cm wide"	"Aristida ramosissima"
3	"Plants perennial; synflorescences 10-30 cm long, 4-26 mm wide"	"Aristida schiedeana"
4	"Central awns spirally coiled at the base"	5
4	"Central awns straight to curved, sometimes loosely contorted, but not spirally coiled, at the base"	6
5	"Lateral awns 1-4 mm long, erect"	"Aristida dichotoma"
5	"Lateral awns 5-13 mm long, spreading"	"Aristida basiramea"
6	"Lateral awns markedly reduced, usually 1/3 or less as long as the central awns"	7
6	"Lateral awns well-developed, usually at least 1/2 as long as the central awn"	21
7	"Panicles 1-6 cm wide, the branches erect-appressed to strongly ascending; axillary pulvini absent or only weakly developed"	8
7	"Panicles 6-45 cm wide, at least the lower branches spreading and with well-developed axillary pulvini"	14
8	"Plants annual; culms often greatly branched above the base"	9
8	"Plants perennial; culms rarely branched above the base"	11
9	"Awns flattened at the base"	"Aristida adscensionis"
9	"Awns terete at the base"	10
10	"Lemmas 2.5-10 mm long; central awns curing up to 100 degrees at the base"	"Aristida longespica"
10	"Lemmas 8-22 mm long; central awns with a semicircular bend at the base"	"Aristida ramosissima"
11	"Collars densely pilose, the hairs 1-3 mm long, often densely tangled and deflexed; blades usually tightly involute, about 0.5 mm in diameter"	"Aristida gypsophila"
11	"Collars usually glabrous or with straight hairs, often with longer hairs at the sides; blades usually flat to loosely involute, sometimes tightly involute"	12
12	"Lateral awns essentially absent; panicle brnches spikelet-bearing to the base; plants of the Florida keys"	"Aristida floridana"
12	"Lateral awns usually present, varying from much shorter than to equaling the cenral awns; pancile branches sometimes naked near the base; plants rarely found east of the Mississippi, not known from Florida"	13
13	"Primary panicle branches 3-6 cm long; lateral awns (1)8-140 mm long"	"Aristida purpurea"
13	"Primary panicle branches 6-16 cm long; lateral awns absent or to 1(3) mm long"	"Aristida schiedeana"
14	"Lateral awns absent or not more than 3 mm long"	15
14	"Lateral awns 3-23 mm long"	18
15	"Central awns often deflexed at a sharp angle when mature; lemma apices often twisted at maturity"	16
15	"Cenral awns usually straight or arcuate; lemma apices not twisted"	17
16	"Blades usually flat, sometimes folder, 1-2 mm wide; plants of juniper, oak, or pine woodlands"	"Aristida schiedeana"
16	"Blades usually tightly involute, about 0.5 mm in diameter; plants of thorn-scrub deserts"	"Aristida gypsophila"
17	"Panicles branches spikelet-bearing to the base; lower glumes longer than the upper"	"Aristida floridana"
17	"Panicle branches usually naked at the base; lower and upper glumes about equally long"	"Aristida ternipes"
18	"Anthers 0.3-1 mm long"	19
18	"Anthers 1.2-3 mm long"	20
19	"Spikelets usually divergent, the pedicels with axillary pulvini; secondary branches usually absent; primary branches 2-6 cm long; lemma apices with 0-2 twists when mature"	"Aristida havardii"
19	"Spikelets usually appressed, the pedicels without axillary pulvini; secondary branches usually well-developed; primary branches 5-13 cm long; lemma apices with 4 or more twists when mature"	"Aristida divaricata"
20	"Collars glabrous or strigillose; blades with scattered hairs 1.5-3 mm long above the ligule on the adaxial surface; lower glumes about equal to or slightly shorter than the upper glumes"	"Aristida ternipes"
20	"Collars pubescent, the hairs 0.2-0.8 mm long; blades mostly glabrous, sometimes scabridulous above the ligule on the adaxial surface; lower glumes slightly longer than the upper glumes"	"Aristida patula"
21	"Blades tightly involute, the adaxial surfaces densely scabrous or densely short pubescent"	"Aristida stricta"
21	"Blades flat or folded and lax or, if involute, the adaxial surfaces neither densely scabrous nor densely short pubescent"	22
22	"Rachis nodes and leaf sheaths usually lanose or floccose, sheaths occasionaly glabrous"	"Aristida lanosa"
22	"Rachis nodes glabrous, scabrous, or with straight hairs; leaf sheaths glabrous, pilose, or floccose"	23
23	"Junction of lemmas with their awn evident; awns disarticulating at maturity"	24
23	"Junction of lemmas with their awn not evident; awns not disarticulating at maturity"	28
24	"Plants perennial"	25
24	"Plants annual"	26
25	"Culms 45-100 cm tall, unbranched or sparingly branched; blades 12-28 cm long"	"Aristida spiciformis"
25	"Culms 10-40 cm tall, much branched; blades usually less than 6 cm long"	"Aristida californica"
26	"Awns divergent but not arcuate or entwined above the column or no column present; cauline internodes pubescent or glabrous"	"Aristida californica"
26	"Awns strongly arcuate, often entwined above the column; cauline internodes glabrous"	27
27	"Glumes 10-17 mm long; lemmas beaked, the beak 2-7 mm long; awns not forming a column at the base; calluses 1-25. mm long"	"Aristida desmantha"
27	"Glumes 20-30 mm long; lemmas not beaked; awns forming a column 8-15 mm long; calluses 3-4 mm long"	"Aristida tuberculosa"
28	"Lemmas terminating in a beak 7-30 mm long; upper glumes awned, the awns 10-12 mm long"	"Aristida spiciformis"
28	"Lemmas not beaked or with a beak less than 7 mm long; upper glumes unawned or with an awn up to 6 mm long"	29
29	"At least the lower primary panicle branches divergent and with axillary pulvini"	30
29	"Lower primary panicle branches (pedicels in racemose plant) appressed, without axillary pulvini"	36
30	"Lateral awns about 1/2 as thick as the central awns"	"Aristida patula"
30	"Lateral awns nearly as thick as the central awns"	31
31	"Panicles narrow and contracted distally, usually only the lower 1 or 2 branches spreading and with an axillary pulvinus; lemma apcies 0.2-0.3 mm wide"	"Aristida purpurea"
31	"Almost all panicle branches spreading and with axillary pulvini; lemma apices 0.1-0.2 mm wide"	32
32	"Anthers 0.8-1 mm long"	33
32	"Anthers 1-3 mm long"	34
33	"Spikelets usually divergent, the pedicels with axillary pulvini; secondary branches absent or almost so; primary branches 2-6 cm long; lemma apices straight or with 1-2 twists when mature"	"Aristida havardii"
33	"Spikelets usually appressed, the pedicels without axillary pulvini; secondary branches usually well-developed; primary branches 5-13 cm long; lemma apices with 4 or more twists when mature"	"Aristida divaricata"
34	"Blades with scattered hairs 1.5-3 mm long at the base on the adaxial surface"	"Aristida ternipes"
34	"Blades glabrous or puberulent at the base on the adaxial surface, hairs, if present shorter than 0.5 mm"	35
35	"Glumes reddish, the lower glumes often shorter than the upper; awns ascending to divaricate, (8)13-140 mm long; terminal spikelets usually appressed and without axillary pulvini"	"Aristida purpurea"
35	"Glumes brownish, equal or unequal; awns spreading to divaricate, 5-15 mm long; terminal spikelets often spreading from axially pulvini"	"Aristida pansa"
36	"Plants with well-developed rhizomes; basal sheaths shredding into threadlike segments at maturity"	"Aristida rhizomophora"
36	"Plants tufted, without rhizomes; basal sheaths not fibrous, not shredding into threadlike segments even when old"	37
37	"Lower inflorescence nodes with only 1 spikelet; inflorescences spicate or racemose"	"Aristida mohrii"
37	"Lower inflorescence nodes with 2 or more spikelets; inflorescences racemose or paniculate"	38
38	"Lower glumes usually 1/3-3/4 as long as the upper glumes"	39
38	"Lower glumes usually more than 3/4 as long as the upper glumes"	41
39	"Plants annual"	"Aristida adscensionis"
39	"Plants perennial"	40
40	"Lemma awns 8-15 mm long; lemmas 5-7 mm long"	"Aristida gyrans"
40	"Lemma awns (8)15-40 mm long; lemmas 6-16 mm long"	"Aristida purpurea"
41	"Plants annual"	42
41	"Plants perennial"	43
42	"Awns flat at the base"	"Aristida adscensionis"
42	"Awns terete at the base"	"Aristida longespica"
43	"Lemma apices prominently twisted for 3-6 mm; blades usually curled at maturity; leaves forming a basal tuft"	"Aristida arizonica"
43	"Lemma apices straight or only slightly twisted; blades usually not curled at maturity; leaves variously distributed"	44
44	"Lower glumes prominently 2-keeled, (7.5)9-13 mm long; central awns 15-40 mm long"	"Aristida palustris"
44	"Lower glumes usually 1-keeled, if 2-keeled, 5-9 mm long; central awns 8-15 mm long"	45
45	"Central awns about twice as thick as the lateral awns, divergent to arcuate-reflexed"	46
45	"Central awns about the same thickness as the later awns, erect to spreading"	47
46	"All 3 awns divergent to reflexed and cotorted at the base; lower rachis nodes usually associated with 2 spikelets (occasionally 1 or 3), 1 pedicellate, the other sessile"	"Aristida simpliciflora"
46	"Lateral awns usually erect to ascending and not contorted at the base; lower rachis noes usually associated with more than 2 spikelets, pedicellate to subsessile"	"Aristida purpurascens"
47	"Lower glumes 1-4 mm longer than the upper glumes"	"Aristida purpurascens"
47	"Lower glumes from shorter than to 1 mm longer than the upper glumes"	48
48	"Culms usually 3-6 mm thick at the base; primary panicle branches 4-20 cm long; lower glumes 1-veined"	"Aristida condensata"
48	"Culms usually 1-4 mm thick at the base; panicles branches 1-5 cm long; lower glumes 1-2-veined"	49
49	"Calluses 0.4-0.8 mm long"	"Aristida purpurascens"
49	"Calluses 1-2 mm long"	"Aristida gyrans"