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| 1 Heads appearing spherical (the ‘visual head’ actually a secondary head aggregated of numerous 1-flowered heads); disk flowers blue (rarely almost white) |
| 1 Heads not spherical; disk flowers pink (rarely yellow). |
| ..2 Stem winged, the wings armed with spines. |
| ....3 Pappus of plumose bristles |
| ....3 Pappus of barbellulate bristles. |
| ......4 Cypselas borne on the surface of the receptacle, intermixed with setiform scales; foliage glabrous or more loosely and sparsely pubescent |
| ......4 Cypselas borne in the pits of the naked honeycombed receptacle; foliage densely white-tomentose |
| ..2 Stem not winged. |
........5 Leaves green with white mottles |
| ........5 Leaves green. |
| ..........6 Disk flowers pink (rarely white) |
| ..........6 Disk flowers yellow. |
| ............ 7 Pappus of numerous plumose bristles |
| ............ 7 Pappus absent or of scales or barbellulate bristles. |
| ............ ..8 Cypselas 4-angled; receptacles bearing subulate scales |
| ............ ..8 Cypselas terete, 20-ribbed; receptacles bearing flattened bristles |