| 1 | Florets yellow |
| 1' | Florets purple, pink or white |
| 2 | Outer phyllaries with purple spinule; plant arachnoid-villose |
| 2' | Outer phyllaries with stiff spine(s); plant thinly pilose, glandular or glabrescent |
| 3 | Stems winged with decurrent leaf-bases; involucral spines slender |
| 3' | Stems not winged; involucral spines stout, rigid |
| 4 | Involucre conspicuously spinose |
| 4' | Involucre unarmed or phyllaries with a very short apical spinule |
| 5 | Pappus present; involucre width 10-15 mm |
| 5' | Pappus lacking; involucre width 3.5-8 mm |
| 6 | Involucre width 6-7(-8) mm |
| 6' | Involucre width 3.5-5(-5.5) mm |
| 7 | Annuals with conspicuously radiant, bright blue marginal florets; pappus lacking |
| 7' | Perennials with thick taproots; marginal florets pink or mauve or conspicuous marginal florets lacking; pappus present |
| 8 | Acaulescent perennial with very short stems, often stems lacking, but rarely up to 20 cm long; capitula solitary or in subsessile clusters of 4-6 |
| 8' | Perennial with numerous stems and capitula |
| 9 | Stem erect; no marginal, radiant florets; ciliate appendages of phyllaries about as long as undivided central part |
| 9' | Stem prostrate or drooping (chasmophyte); with conspicuous marginal, radiant florets; ciliate appendages of phyllaries much shorter than undivided central part |
| 10 | Leaves finely pinnatisect; phyllaries with inconspicuously ciliate appendages; pappus 3-4(-5) mm long |
| 10' | Basal leaves lyrate, cauline leaves spathulate to denticulate or lobed; phyllaries with well-developed cilia; pappus up to 2 mm long |
