| | 1. Well developed ray flowers 0; ligules of pistillate flowers 0 or pistillate flowers 0 |
| |
| | 2. Disk flowers 4; corollas 3-lobed |
| P. alsinoides |
| | 2' Disk flowers 6–34; corollas 5-lobed |
| P. exilis subsp. exilis |
| | 1' Well developed ray flowers present; ligules evident |
| |
| | 3. Ray flowers white; pappus bristles present or 0 |
| |
| | 4. Ray flowers 7–16; peduncles glabrous to short-hairy |
| P. bellidiflora |
| | 4' Ray flowers 0–3; peduncles soft-shaggy-hairy |
| P. exilis subsp. aeolica |
| | 3' Ray flowers generally yellow; pappus bristles present |
| |
| | 5. Ray flowers 7–12, disk flowers 10–23; largest leaves < 2.5 cm |
| P. fragilis |
| | 5' Ray and disk flowers > 12; largest leaves 2.5–5.5 cm |
| |
| | 6. Phyllaries ovate-elliptic, glabrous or sparsely short-hairy; pappus bristles 5–8 |
| P. aurea |
| | 6' Phyllaries lanceolate, soft-shaggy-hairy; pappus bristles 8–12 |
| P. lyonii
|