| 1. Leaf scale-like, << 1 mm |
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| 2. Stem canescent, especially at tip, reddish to green; spike with 23(7) fertile internodes; on Acacia, Cercidium, Larrea (rarely), Olnyea, Prosopis; < 1200 m |
| P. californicum |
| 2' Stem glabrous, ± green or yellow-green; spike with 12 fertile internodes; on Calocedrus, Juniperus; 13002600 m |
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| 3. Stem generally erect, internodes 510(12) mm; on Juniperus; 17002600 m |
| P. juniperinum |
| 3' Stem often ± pendent in age, internodes (6)1020 mm; on Calocedrus; 13001900 m |
| P. libocedri |
| 1' Leaf with blade, generally 547 mm |
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| 4. Leaf length generally < 1.5 × width, 1547 mm, generally > 20 mm; stem generally short-hairy, at least at tip; spike with 25(7) fertile internodes, pistillate 615(20)-flowered; on woody dicots |
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| 5. Leaf 3042 mm, 1523 mm wide, generally glabrous, if hairy not very densely so; fruit glabrous; staminate fertile internodes 25(7), generally 3035-flowered, pistillate 24(5), 610(20)-flowered; on woody dicots other than Quercus (especially Alnus, Fraxinus, Juglans, Platanus, Populus, Prosopis, Robinia, Salix); flower DecemberMarch; < 1200 m |
| P. macrophyllum |
| 5' Leaf 1547 mm, 1025 mm wide, very densely short-hairy; fruit short-hairy near tip; staminate fertile internodes 24, generally 2530-flowered, pistillate 2(3), generally 1015-flowered; on generally Quercus, less often other associated woody dicots (e.g. Adenostoma, Arctostaphylos, Rhus, Umbellularia); flower July-September; 602100 m |
| P. villosum |
| 4' Leaf length generally > 3 × width, 525 mm (generally < 20 mm); stem glabrous; spike with generally 1 fertile internode, pistillate 2-flowered; on conifers |
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| 6. Leaf generally 1015 mm, 25 mm wide; on Cupressus, Juniperus (reported on Pinus monophylla); 2002300 m |
| P. densum |
| 6' Leaf generally 525 mm, 58 mm wide; on Abies concolor; 14002500 m |
| P. pauciflorum
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