| | 1. Cup scales thin, flat; bark dark gray or black; acorn shell woolly inside |
| |
| | 2. Leaf moderately to deeply lobed, sinuses between lobes 1/2+ width to midrib, lobes 1–4-toothed, teeth generally bristle-tipped; plants deciduous |
| Q. kelloggii |
| | 2' Leaf entire to toothed, teeth abruptly pointed to spine-tipped, not bristle-tipped; plants evergreen |
| |
| | 3. Leaf upper surface convex, margin sometimes inrolled, obscuring marginal teeth, lower vein axils often hair-tufted, blade generally widely elliptic to round; fruit maturing in 1 year (on current twig) |
| Q. agrifolia |
| | 4. Leaf lower surface glabrous to sparsely hairy (except vein axils) |
| var. agrifolia |
| | 4' Leaf lower surface densely tomentose |
| var. oxyadenia |
| | 3' Leaf ± flat, margin not inrolled, lower surface glabrous, blade generally lanceolate to oblong; fruit maturing in 2 years (on previous year's growth) |
| |
| | 5. Leaves 3–9 cm; leaf lower surface generally ± dull, olive-green; nut oblong below middle, abruptly tapered to tip |
| Q. parvula |
| | 6. Shrub 1–3 m; n Channel Islands, n South Coast |
| var. parvula |
| | 6' Tree < 17 m; w San Francisco Bay Area, Outer South Coast Ranges |
| var. shrevei |
| | 5' Leaves 2–5 cm; leaf lower surface generally ± shiny, yellow-green; nut gradually tapered from below middle to tip |
| Q. wislizeni |
| var. frutescens |
| var. wislizeni |
| | 1' Cup scales generally thick, ± flat to generally clearly tubercled; bark light gray to whitish; acorn shell glabrous to woolly inside |
| |
| | 8. Acorn shell ± woolly inside; fruit maturing in 2 years; plants evergreen |
| |
| | 9. Leaves mostly 3–8 cm; acorn cup thick; generally tree |
| |
| | 10. Leaf lateral veins not clearly impressed on upper surface, lower surface golden-hairy, becoming glabrous |
| Q. chrysolepis |
| | 10' Leaf lateral veins impressed on upper surface, lower surface densely tomentose, becoming sparsely tomentose — Channel Islands |
| Q. tomentella |
| | 9' Leaves mostly 1–3.5 cm; acorn cup thin; shrub (or tree < 7 m) |
| |
| | 11. Twigs very stiff, rigid; leaf margin ± wavy, clearly spine-toothed; blade elliptic to round-ovate; plants 2–6 m, erect |
| Q. palmeri |
| | 11' Twigs pliable; leaf margin generally entire, sometimes irregularly serrate, not spine-tipped; blade oblong to ovate; plants < 1.5 m, prostrate to spreading |
| Q. vacciniifolia |
| | 8' Acorn shell glabrous inside; fruit maturing in 1 year; plants evergreen or deciduous |
| |
| | 12. Leaf lobed, sinuses between lobes generally > 1/4 distance from midrib to lobe tip; plants deciduous |
| |
| | 13. Leaf moderately to deeply lobed, some sinuses between lobes generally > 1/2 distance to midrib; upper surface ± shiny, dark green |
| |
| | 14. Acorn cup 10–30 mm deep, scales all clearly tubercled; nut 30–50 mm, generally long-conic in outline, gradually tapered to pointed tip (also see 17') |
| Q. lobata |
| | 14' Acorn cup 4–9 mm deep, upper scales ± flat, lower scales slightly tubercled; nut 20–30 mm, ovoid to subspheric, tip ± rounded |
| Q. garryana |
| | 15. Shrub 1–5 m; petiole 5–20 mm; leaf blade 4–9 cm |
| var. breweri |
| | 15' Tree 8–20 m; petiole 10–25 mm; leaf blade 7–14 cm |
| var. garryana |
| | 13' Leaf weakly lobed, sinuses between lobes generally < 1/2 distance to midrib; upper surface generally dull, green to bluish green |
| |
| | 16. Upper leaf surface green; acorn cup scales clearly tubercled; Channel Islands |
| Q. ×macdonaldii |
| | 16' Upper leaf surface bluish or grayish green; acorn cup scales slightly tubercled; mainland |
| |
| | 17. Small tree (sometimes shrubby), semi-evergreen; leaves 1.5–5 cm, generally irregularly and coarsely toothed, upper surface bluish or grayish green |
| 2 Q. ×alvordiana |
| | 17' Tree, deciduous; leaves generally 3–6 cm, slightly lobed or subentire, upper surface bluish green |
| Q. douglasii |
| | 12' Leaf entire to toothed, not lobed; plants evergreen |
| |
| | 18. Leaves generally 7–11 cm, clearly serrate (teeth 20–32), lateral veins 20–28, prominent; stipules persistent, > 10 mm, silky-hairy |
| Q. sadleriana |
| | 18' Leaves 1–6 cm, entire to dentate, lateral veins generally < 20, not prominent; stipules early deciduous, < 10 mm, not silky-hairy |
| |
| | 19. Trees generally > 5 m; leaves 2–6 cm, oblong to obovate, entire or slightly toothed, upper surface often bluish green |
| |
| | 20. Tree < 6(10) m; leaves generally irregularly toothed to subentire, upper surface green to bluish green, ± glossy to dull |
| 2 Q. ×acutidens |
| | 20' Tree 5–18 m; leaves generally entire or wavy-dentate, upper surface blue-green, dull |
| Q. engelmannii |
| | 19' Shrub generally < 5 m; leaves 1–5 cm, elliptic to ovate or roundish, variously toothed, upper surface generally green |
| |
| | 21. Leaf 2-colored, upper surface yellow- or gray-green, lower surface whitish, densely finely tomentose, hairs obscuring lateral veins |
| Q. cornelius-mulleri |
| | 21' Leaf 1–2-colored, upper surface green to gray- or bluish green, lower surface generally green, not densely tomentose, hairs not obscuring lateral veins |
| |
| | 22. Leaf generally oblong to obovate, margin wavy to obtusely toothed — Peninsular Ranges |
| 2 Q. ×acutidens |
| | 22' Leaf elliptic to ovate or roundish, margin clearly toothed, teeth abruptly pointed to spine-tipped |
| |
| | 23. Acorn cup thin, scales ± flat to slightly tubercled; upper leaf surface gray- or bluish green, dull |
| |
| | 24. Acorn stalked (stalk < 15 mm), nut cylindric-ovoid to elliptic in outline, abruptly tapered at tip, 12–23 mm, generally yellow-brown; leaves oblong to elliptic, regularly spine-toothed — eastern Desert Mountains |
| Q. turbinella |
| | 24' Acorn sessile, nut conic-ovoid, gradually tapered to tip, 20–40 mm, generally dark brown; leaves oblong to elliptic or obovate, irregularly toothed, teeth blunt to weakly spiny |
| |
| | 25. Shrub or small tree; leaves 1.5–5 cm, marginal teeth not spiny, upper surface bluish to grayish green |
| 2 Q. ×alvordiana |
| | 25' Shrub; leaves 1.3–2.8 cm, irregularly spine-toothed, upper surface grayish green |
| Q. john-tuckeri |
| | 23' Acorn cup thick, scales tubercled; upper leaf surface generally green, ± shiny (sometimes dull in Q. durata) |
| |
| | 26. Upper leaf surface convex, margin often inrolled, obscuring teeth, dull |
| Q. durata |
| | 27. Upper leaf surface strongly convex; lower leaf surface short-hairy; generally serpentine soils, North Coast Ranges, n Sierra Nevada Foothills, South Coast Ranges |
| var. durata |
| | 27' Upper leaf surface slightly convex; lower leaf surface densely short-hairy when young; nonserpentine soils, s San Gabriel Mountains |
| var. gabrielensis |
| | 26' Upper leaf surface flat to ± wavy, not convex, margin generally not inrolled, ± shiny |
| |
| | 28. Fruit 10–30 mm; acorn cup thick, 12–20 mm wide, scales strongly tubercled; nut ovoid; chaparral, 300–1500 m |
| Q. berberidifolia |
| | 28' Fruit < 20 mm; acorn cup thin, 8–15 mm wide, scales slightly to moderately tubercled; nut conic-ovoid; chaparral or coastal-sage scrub, < 200 m |
| Q. dumosa
|