| 1. Stems glabrous, puberulent, or gland-dotted |
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| 2. Herbage gland-dotted; corollas yellow |
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| 3. Involucres 68 mm, obconic; phyllaries weakly vertically ranked, tips not swollen |
| C. paniculatus |
| 3' Involucres 79.5 mm, cylindric; phyllaries strongly vertically ranked, tips swollen, green |
| C. teretifolius |
| 2' Stems (and generally leaves) not gland-dotted; corollas generally yellow (white) |
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| 4. Corollas white; leaves gland-dotted |
| C. albidus |
| 4' Corollas yellow; leaves not gland-dotted |
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| 5. Fruit glabrous; leaves flat, rigid, persistent |
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| 6. Involucres generally 1013 mm; phyllaries strongly keeled |
| C. depressus |
| 6' Involucres generally 1215 mm; phyllaries not keeled |
| C. gramineus |
| 5' Fruit (generally densely) hairy; leaves generally twisted |
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| 7. Heads overtopped by leaves; flowers 23(4) per head |
| C. humilis |
| 7' Heads not overtopped by leaves; flowers 3+ per head |
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| 8. Phyllaries acuminate to bristle-tipped; leaves < 1 mm wide |
| C. greenei |
| 8' Phyllaries obtuse to acute; leaves 110 mm wide |
| C. viscidiflorus |
| 9. Upper stems (and generally leaves) hairy |
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| 10. Stems bristly near inflorescence; leaves > 2 mm wide, ± rough-hairy |
| subsp. lanceolatus |
| 10' Herbage finely puberulent; leaves 12(4) mm wide, glabrous |
| subsp. puberulus |
| 9' Stems glabrous; leaves glabrous (except generally ciliate) |
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| 11. Leaves ± 1 mm wide; flowers 34(5) per head; involucre ± obconic |
| subsp. axillaris |
| 11' Leaves 110 mm wide; flowers generally 4+ per head; involucre cylindric |
| subsp. viscidiflorus |
| 1' Stems tomentose to felted |
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| 12. Phyllaries long-acuminate, weakly keeled; inflorescence generally raceme-like; heads 518-flowered |
| C. parryi |
| 13. Leaves generally > 3 cm, > 5 mm wide |
| subsp. latior |
| 13' Leaves generally < 3 cm, 4 mm wide or less |
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| subsp. imulus |
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| 15. Leaves oblanceolate, glands short-stalked |
| subsp. asper |
| 15' Leaves linear to oblanceolate, stalked glands 0 |
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| 16. Heads 13 per inflorescence; corolla 89 mm |
| subsp. monocephalus |
| 16' Heads many per inflorescence; corolla > 9 mm |
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| 17. Phyllaries tips recurved; corolla 1011 mm |
| subsp. nevadensis |
| 17' Phyllaries straight; corolla 1112.5 mm |
| subsp. vulcanicus |
| 12' Phyllaries obtuse to acute, strongly keeled; inflorescence generally panicle-like; heads 5-flowered |
| C. nauseosus |
| 18. Involucre subglabrous to tomentose; stems generally whitish; leaves generally dark green to grayish white |
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| 19. Fruit glabrous except white-hair-tufted at top |
| subsp. washoensis |
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| subsp. bernardinus |
| 20' Involucre 710(11) mm |
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| 21. Corolla lobes 12 mm; style appendage > stigma |
| subsp. albicaulis |
| 21' Corolla lobes 0.51 mm; style appendage < stigma |
| subsp. hololeucus |
| 18' Involucre glabrous (outer phyllaries sometimes ciliate or scaly-margined); stems greenish or brownish; leaves greenish yellow or 0 |
| |
| subsp. leiospermus |
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| 23. Leaves 13 mm wide, 15-veined; involucre > 10 mm |
| subsp. bernardinus |
| 23' Leaves 1 mm wide or less, 1-nerved; involucre < 10 mm |
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| 24. Phyllaries abruptly pointed, recurved |
| subsp. ceruminosus |
| 24' Phyllaries acute, erect |
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| 25. Involucres 610 mm; stems generally leafy |
| subsp. consimilis |
| 25' Involucres 8.512 mm; stems often leafless |
| subsp. mohavensis
|