| | 1. Annual; remains of previous years growth not present |
| |
| | 2. Lowest lemma ± 2 mm; lemma tip obtuse to truncate |
| P. parishii |
| | 2' Lowest lemma 3.5–4 mm; lemma tip acute |
| P. simplex |
| | 1' Perennial; previous years leaves persistent |
| |
| | 3. Spikelet stalk glabrous or sparsely fine scabrous |
| |
| | 4. Lemma margin near tip uniformly scabrous-serrate at 10×; lowest floret anthers 1.5–2 mm; Klamath Ranges (Shasta Co.) |
| P. howellii |
| | 4' Lemma margin near tip entire or sparsely fine-scabrous at 10×; lowest floret anthers < 1 mm; North Coast |
| P. pumila |
| | 3' Spikelet stalk uniformly scabrous |
| |
| | 5. Lemma tip obtuse to truncate |
| |
| | 6. Lowest floret lemma 1.5–2 mm; lower inflorescence branches spreading to reflexed in fruit |
| P. distans |
| | 6' Lowest floret lemma 2–4 mm; lower inflorescence branches erect to reflexed in fruit |
| |
| | 7. Lowest floret lemma 3.5–4 mm; lower inflorescence branches erect in fruit; coastal habitats |
| 2 P. nutkaensis |
| | 7' Lowest floret lemma 2–3.5 mm; lower inflorescence branches erect to reflexed in fruit; California Floristic Province, Great Basin Floristic Province, generally inland |
| 2 P. nuttalliana |
| |
| | 8. Lowest floret lemma 3.5–4 mm; cauline leaf blade 2–3 mm wide when flat; lower inflorescence branches erect in fruit; coastal habitats |
| 2 P. nutkaensis |
| | 8' Lowest floret lemma 2–3.5 mm; cauline leaf blade 1–4 mm wide when flat; lower inflorescence branches erect to reflexed in fruit; inland habitats |
| |
| | 9. Cauline leaf blade inrolled, 1–2 mm wide when flat; lemma margin near tip entire to uniformly scabrous-serrate at 10×; inflorescence generally < 10 cm |
| P. lemmonii |
| | 9' Cauline leaf blade flat to inrolled, 1–4 mm wide when flat; lemma margin near tip scabrous-serrate at 10×; inflorescence generally > 10 cm |
| 2 P. nuttalliana
|