| 1. Basal segment of awn hairy, some hairs > 1 mm; callus sharp |
| |
| 2. Lowest hairs on awn > upper lemma hairs |
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| 3. Awn with 1 bend; uppermost ligule 0.31 mm, long ciliate |
| A. speciosum |
| 3' Awn with 2 bends; uppermost ligule 27 mm, glabrous |
| |
| 4. Inflorescence 1530 cm; uppermost ligule 24 mm, opaque |
| A. latiglume |
| 4' Inflorescence 713 cm; uppermost ligule 37 mm, translucent |
| A. thurberianum |
| 2' Lowest hairs on awn < upper lemma hairs |
| |
| 5. Palea 2/33/4 lemma length |
| A. nevadense |
| 5' Palea 1/31/2 lemma length |
| A. occidentale |
| 6. All awn segments hairy |
| subsp. occidentale |
| 6' Lower awn segments hairy, upper glabrous |
| |
| 7. Hairs of lemma tip = hairs at awn base |
| subsp. californicum |
| 7' Hairs of lemma tip > hairs at awn base |
| subsp. pubescens |
| 1' Basal segment of awn scabrous; callus sharp or blunt |
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| 8. Hairs of lemma tip 27 mm |
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| 9. Awn 311 mm, straight, readily deciduous |
| |
| 10. Inflorescence open, branches and pedicels widely spreading |
| A. hymenoides |
| 10' Inflorescence dense, branches and pedicels ascending |
| A. webberi |
| 9' Awn 1344 mm, with 1 or 2 bends, persistent |
| |
| 11. Hairs of lemma tip = hairs at lemma midpoint |
| A. pinetorum |
| 11' Hairs of lemma tip 17 mm, > hairs at midpoint; awn with 1 or 2 bends |
| |
| 12. Awn bent twice; basal leaf blade 2.57 mm |
| A. coronatum |
| 12' Awn bent once; basal leaf blade 23 mm |
| A. parishii |
| 8' Hairs of lemma tip < 2 mm |
| |
| 13. Distal segment of awn wavy |
| A. aridum |
| 13' Distal segment of awn straight |
| |
| 14. Palea 1/32/3 lemma length |
| |
| 15. Internodes above middle with reflexed hairs |
| A. diegoense |
| 15' Internodes generally glabrous or inconspicuously hairy at nodes |
| A. nelsonii subsp. dorei |
| 14' Palea > 3/4 lemma length |
| |
| 16. Lemma tip 2-toothed, awn-like teeth 12 mm; stems 615 dm |
| A. stillmanii |
| 16' Lemma tip 2-toothed or not, teeth < 1 mm; stems 1.59 dm |
| |
| 17. Lemma tip with thick lobe ± 0.1 mm; floret 5.57 mm, somewhat compressed |
| A. lemmonii subsp. lemmonii |
| 17' Lemma tip with membranous lobe 0.21 mm; floret 4.56 mm, cylindric |
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| 18. Palea thick, stiff, veins evident |
| A. brachychaetum |
| 18' Palea thin, flexible, veins obscure |
| A. lettermanii
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