| 1 (1) |
Robust or sturdy perennials; caespitose or with a creeping, ligneous rhizome (but, first-season plants of C. aucheri resemble annuals, 4). |
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(1) |
| + |
Short-lived perennials or slender annuals; roots fibrous. |
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(2) |
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| 2 (1) |
Leaf blades reduced; Primary rays and foliose involucral bracts and primary rays up to 20. |
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22 C. alternifolius |
| + |
Leaf blades well developed; primary rays and involucral bracts up to 5. |
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(3) |
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| 3 (2) |
Caespitose plants with tillers, old dark tillers remain tightly attached to base of new shoots; inflorescence a single head with 4-20 compressed spikes. |
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28 C. niveus |
| + |
Rhizome long-creeping (mostly deep in sand) giving rise to aerial shoots, or plants caespitose; inflorescence mostly a multiple spike or formed by several capitula, sometimes in stunted plants (notably C. conglomeratus subsp. curvulus) inflorescence reduced to few or single spike. |
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(4) |
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| 4 (3) |
Nuts winged; roots tomentose. |
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27 C. aucheri |
| + |
Nuts not winged; roots tomentose or glabrous. |
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(5) |
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| 5 (5) |
Caespitose plants or rhizome short; roots tomentose. |
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(5) |
| + |
Rhizome long-creeping, roots glabrous. |
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23 C. arenarius |
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| 6 |
Plants tall; inflorescence a compact globose head. |
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26 C. pachyrhizus |
| + |
Plants small; inflorescence an anthelodium. |
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(7) |
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| 7 (6) |
Plants rather small and slender; basal sheaths soft; roots glabrous. |
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24 C. atkinsoni |
| + |
Plants rigid; basal sheeths hard; roots tomentose. |
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25 C. conglomeratus |
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| 8 (8) |
Plants 10-40 cm; glumes obtuse or acute not recurved. |
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(8) |
| + |
Plants 4-15 cm; glumes apiculate, conspicuously recurved. |
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(9) |
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| 9 (9) |
Distal partial inflorescence with up to 15 spikes; ligule 0. |
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(9) |
| + |
Distal partial inflorescence with up to 100 crowded spikes; ligule present. |
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(10) |
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| 10 (9) |
Glumes 1.3-1.5 mm, straight; nut 0.5-0.7 mm, reticulate. |
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29 C. haspan |
| + |
Glumes 0.7-0.9 mm, rather cymbiform; nut 0.4-0.5 mm, papillose. |
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30 C. tenuispica |
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| 11 |
Spikes in globose heads of up to 100 spikes; glumes distinctly cymbiform, obtuse. |
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31 C. difformis |
| + |
Spikes in digitate groups of up to 40 spikes; glumes not distinctly cymbiform, acute. |
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32 C. fuscus |
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| 12 |
Glumes truncate, with 3-nerved keel and nerveless sides. |
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33 C. cuspidatus |
| + |
Glumes attenuate, sides conspicuously nerved. |
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(13) |
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| 13 (12) |
Glumes 2.2-3 mm, sides with 2-3 nerves; stamens 3. |
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35 C. steadii |
| + |
Glumes 1.5-2.3 mm, sides with 3-4 nerves; stamens 1-2. |
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34 C. squarrosus |
