| 1. Dioecious; spikelets staminate or pistillate; reduced, sterile pistils sometimes present (subg. Leucopoa) rhizomes short; lemma awnless |
| F. kingii |
| 1' Bisexual; florets generally bisexual (subg. Festuca) |
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| 2. Basal lobes of leaf blade prominent, ± clasping stem |
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| 3. Basal lobes hairy; lemma awn generally 0.51.5 mm |
| F. arundinacea |
| 3' Basal lobes glabrous; lemma awn << 0.5 mm or 0 |
| F. pratensis |
| 2' Basal lobes of leaf blade, if any, not clasping stem |
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| 4. Leaf sheath closed, ± reddish, generally with downward-pointing hairs; rhizomes often present |
| F. rubra |
| 4' Leaf sheath open at least half its length, generally green, glabrous; rhizomes 0 |
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| 5. Plant > 3 dm; stems densely clumped with conspicuous dead leaf sheaths at plant base |
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| 6. Leaf collar generally hairy; ovary tip hairy |
| F. californica |
| 6' Leaf collar and ovary tip glabrous |
| F. idahoensis |
| 5' Plants < 3 dm (> 3.5 dm in F. elmeri, F. subulata, F. trachyphylla, F. viridula); if stems densely clumped, dead leaf sheaths not conspicuous |
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| 7. Leaf blade flat or loosely rolled, > 2 mm wide |
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| 8. Lemma base long, with a tuft of hairs |
| F. subuliflora |
| 8' Lemma base very short, glabrous |
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| 9. Lemma prominently scabrous; awn subterminal from between 2 short teeth |
| F. elmeri |
| 9' Lemma sparsely scabrous; awn terminal |
| F. subulata |
| 7' Leaf blade folded (except F. viridula), < 2 mm wide |
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| F. occidentalis |
| 10' Lemma awns 0.52.5 mm |
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| F. viridula |
| 11' Spikelets 2.59 mm (F. ovina complex; separations may prove difficult) |
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| 13. Inflorescence 15 cm; anthers < 2 mm; high montane, native |
| F. saximontana var. purpusiana |
| 13' Inflorescence 313 cm; anthers 23 mm; disturbed places, naturalized |
| F. trachyphylla |
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| 14. Inflorescence generally unbranched; ovary glabrous |
| F. brachyphylla subsp. coloradensis |
| 14' Inflorescence short-branched at lowest node; ovary with a few stiff hairs |
| F. minutiflora
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