| 1. Lower stems densely hairy |
| A. californica var. californica |
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| 3. Lemma awns < 2.5 cm; glumes 510 mm |
| A. adscensionis |
| 3' Lemma awns > 3.5 cm; glumes 2034 mm |
| A. oligantha |
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| 4. Base of 1° inflorescence branches abruptly spreading or ascending from main axis |
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| 5. Lower inflorescence branches ascending, upper appressed |
| A. purpurea var. parishii |
| 5' All inflorescence branches spreading |
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| 6. Leaf blade base glabrous; lemma tip much twisted; anthers ± 1 mm |
| A. divaricata |
| 6' Leaf blade base sparsely long-hairy; lemma tip slightly twisted or straight; anthers 12 mm |
| A. ternipes var. hamulosa |
| 4' Base of 1° inflorescence branches appressed to main axis, tips sometimes spreading or ascending |
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| A. purpurea |
| 8. Upper glume generally > 16 mm; lemma ± linear |
| var. longiseta |
| 8' Upper glume generally < 16 mm; lemma gradually tapered to tip |
| var. purpurea |
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| 9. Mature inflorescence branches and spikelet stalks slender, curving to drooping, appearing S- or U-shaped |
| var. purpurea |
| 9' Mature inflorescence branches and spikelet stalks generally stiff, straight, erect to spreading |
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| 10. Tip of lemma generally < 0.2 mm wide; awns delicate, generally < 0.2 mm wide at base |
| var. nealleyi |
| 10' Tip of lemma generally > 0.2 mm wide; awns stiff, generally > 0.2 mm wide at base |
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| 11. Inflorescence generally 314 cm; leaf blade generally < 10 cm |
| var. fendleriana |
| 11' Inflorescence generally 1530 cm; leaf blade generally > 10 cm |
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| 12. Inflorescence dense, reddish, fading to straw-colored; lower branches with 818 spikelets |
| var. parishii |
| 12' Inflorescence somewhat loose, tan to brown, fading to straw-colored; lower branches with 210 spikelets |
| var. wrightii
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