| | 1. Leaf scale-like, << 1 mm |
| |
| | 2. Stem canescent, especially at tip, reddish to green; spike with 2–3(7) fertile internodes; on Acacia, Cercidium, Larrea (rarely), Olnyea, Prosopis; < 1200 m |
| P. californicum |
| | 2' Stem glabrous, ± green or yellow-green; spike with 1–2 fertile internodes; on Calocedrus, Juniperus; 1300–2600 m |
| |
| | 3. Stem generally erect, internodes 5–10(12) mm; on Juniperus; 1700–2600 m |
| P. juniperinum |
| | 3' Stem often ± pendent in age, internodes (6)10–20 mm; on Calocedrus; 1300–1900 m |
| P. libocedri |
| | 1' Leaf with blade, generally 5–47 mm |
| |
| | 4. Leaf length generally < 1.5 × width, 15–47 mm, generally > 20 mm; stem generally short-hairy, at least at tip; spike with 2–5(7) fertile internodes, pistillate 6–15(20)-flowered; on woody dicots |
| |
| | 5. Leaf 30–42 mm, 15–23 mm wide, generally glabrous, if hairy not very densely so; fruit glabrous; staminate fertile internodes 2–5(7), generally 30–35-flowered, pistillate 2–4(5), 6–10(20)-flowered; on woody dicots other than Quercus (especially Alnus, Fraxinus, Juglans, Platanus, Populus, Prosopis, Robinia, Salix); flower December–March; < 1200 m |
| P. macrophyllum |
| | 5' Leaf 15–47 mm, 10–25 mm wide, very densely short-hairy; fruit short-hairy near tip; staminate fertile internodes 2–4, generally 25–30-flowered, pistillate 2(–3), generally 10–15-flowered; on generally Quercus, less often other associated woody dicots (e.g. Adenostoma, Arctostaphylos, Rhus, Umbellularia); flower July-September; 60–2100 m |
| P. villosum |
| | 4' Leaf length generally > 3 × width, 5–25 mm (generally < 20 mm); stem glabrous; spike with generally 1 fertile internode, pistillate 2-flowered; on conifers |
| |
| | 6. Leaf generally 10–15 mm, 2–5 mm wide; on Cupressus, Juniperus (reported on Pinus monophylla); 200–2300 m |
| P. densum |
| | 6' Leaf generally 5–25 mm, 5–8 mm wide; on Abies concolor; 1400–2500 m |
| P. pauciflorum
|