| | 1. Perennial; stem prostrate, mat-forming; taproot > 3 mm diam; flower sparsely hairy near tip, hairs ± straight |
| P. franciscana |
| | 1' Annual; stem ± erect; taproot < 1 mm diam; flower ± moderately hairy on lower 1/2, hairs hooked or tightly coiled |
| |
| | 2. Stem 0.5–2 cm, ± concealed by leaves; flower 1, axillary, 4.2–5 mm; sepals awned from back (tip above awn 1–1.5 mm), awn 1–1.5 mm; sepal margin scarious, 0.5–1 mm wide |
| P. ahartii |
| | 2' Stem 2–15 cm, readily visible between leaves; flowers 3–12, axillary, 2–2.5 mm; sepals awned at tip, awn 0.6–0.9 mm; sepal margin scarious, 0.1–0.2 mm wide |
| P. echinulata var. echinulata
|