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| 2. Lemma awned, awn 13 cm, lemma 2.56 mm |
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| 3. Lemma generally 4.56 mm; inflorescence branches closely appressed, < 1.5 cm wide; glumes generally 12 mm |
| M. appressa |
| 3' Lemma generally 2.54.5 mm; inflorescence branches spreading to ascending, 15 cm wide; glumes generally < 1 mm |
| 2 M. microsperma |
| 2' Lemma abruptly pointed, point < 1 mm, or awn 0; lemma < 2.5 mm |
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| 4. Inflorescence narrow, < 1 cm wide; branches closely appressed; stems often rooting at lower nodes |
| 2 M. filiformis |
| 4' Inflorescence open, 1.58 cm wide; branches reflexed to ascending; stems not rooting at lower nodes |
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| 5. Inflorescence branches stiffly reflexed ± 90° from axis; glumes glabrous; ligule teeth 2, 1 on each side |
| M. fragilis |
| 5' Inflorescence branches ascending < 80° from axis; glume tip short-hairy; ligule truncate to obtuse, irregularly short-toothed |
| M. minutissima |
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| 6. Lemma awn 0 or short-pointed, point < 1 mm |
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| 7. Inflorescence 514 cm wide, open, branches spreading |
| M. asperifolia |
| 7' Inflorescence < 4 cm wide, narrow, branches ascending to appressed |
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| 8. Rhizomes creeping, ± scaly; stems ± decumbent |
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| 9. Glumes 2.54 mm, ± = lemma; lower half lemma short-soft-hairy |
| 2 M. californica |
| 9' Glumes 0.51.8 mm, ± 1/2 lemma length; lemma glabrous to ± scabrous |
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| 10. Ligule generally 12.5 mm; inflorescence axis generally obscured by branches, spikelets |
| M. richardsonis |
| 10' Ligule generally < 1 mm; inflorescence axis generally visible between branches |
| M. utilis |
| 8' Rhizomes 0; stems clumped or decumbent and ± rooting at the nodes |
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| 11. Blade < 4 cm; lemma generally < 2 mm; stems generally < 3 dm |
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| 12. Lemma short-awned, awn < 1 mm; glumes 0.51.2 mm; ligule 12.5 mm, obtuse to acute |
| 2 M. filiformis |
| 12' Lemma awn 1.55 mm; glumes < 0.5 mm; ligule < 0.5 mm, truncate |
| 2 M. schreberi |
| 11' Blade > 5 cm; lemma generally > 2.5 mm; stems 215 dm |
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| 13. Inflorescence < 15 cm, 1.54 cm wide; branches loosely flowered |
| M. jonesii |
| 13' Inflorescence 1560 cm, < 1.2 cm wide; branches densely flowered |
| M. rigens |
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| 14. Inflorescence open, 615 cm wide, branches spreading |
| M. porteri |
| 14' Inflorescence < 5 cm wide, branches ascending to appressed |
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| 15. Glumes 1 or 2, generally < 0.5 mm, vein 0 |
| 2 M. schreberi |
| 15' Glumes 2, generally > 0.5 mm, vein evident |
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| 16. Rhizome generally scaly, creeping |
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| 17. Blade generally rolled, < 2 mm wide; anther purple, 1.53 mm |
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| 18. Lemma, palea short-soft-hairy on lower half; stems loosely clumped, decumbent |
| 2 M. arsenei |
| 18' Lemma base sparsely short-hairy; palea glabrous to ± scabrous; stems erect, ± rooting at lower nodes |
| 2 M. pauciflora |
| 17' Blade generally flat, > 2 mm wide; anther yellow, generally < 1.5 mm |
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| 19. Hairs at lemma base 23.5 mm |
| M. andina |
| 19' Hairs at lemma base < 1.5 mm |
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| 20. Lemma awn generally < 2.2 mm; anther 11.5 mm |
| 2 M. californica |
| 20' Lemma awn 2.59 mm; anther < 0.5 mm |
| M. mexicana |
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| 21. Upper glume 3-veined, 3-toothed |
| M. montana |
| 21' Upper glume generally 1-veined, obtuse, acute, or awned |
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| 22. Glumes generally < 1.5 mm, obtuse; cleistogamous spikelets generally present in lowermost stem axils |
| 2 M. microsperma |
| 22' Glumes generally 1.53.5 mm, acute, acuminate, or awned; cleistogamous spikelets 0 |
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| 23. Lemma, palea short-soft-hairy on lower half; stems loosely clumped, decumbent |
| 2 M. arsenei |
| 23' Lemma base sparsely short-hairy; palea glabrous to ± scabrous; stems erect, ± rooting at lower nodes |
| 2 M. pauciflora
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