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Key to families | Table of families and genera

Specimen numbers are hyperlinked to records in the Consortium of California Herbaria data view where possible. Taxa are hyperlinked to entries in the Jepson Interchange via the "[Online Interchange]" link.



Thomas J. Rosatti & John M. Tucker

Evergreen or not. Leaf: stipules small, generally early-deciduous. Staminate inflorescence: catkins, 1–several, pendent, slender, proximal on twig. Pistillate inflorescence: in distal leaf axils, short-stalked; flower generally 1. Staminate flower: stamens 4–10. Pistillate flower: calyx minute, generally 6-lobed; ovary enclosed by involucre. Fruit: nut 1, partly enclosed by cup-like involucre (cup) with appressed scales (nut and cup = acorn), remnants of perianth and style persistent as small point at tip; scales tubercled to not; mature in years 1 (on younger stems) or 2 (on older stems).
± 600 species: northern hemisphere, to northern South America, India. (Latin: ancient name for oak) [Manos et al. 1999 Molec Phylogen Evol 12:333–349] Many named hybrids; those (3) treated here form widespread populations; most others occur as single individuals, and some but not all of these are mentioned here, under the first parent treated (alphabetically). Reproduction of many species declining due to habitat degradation or loss as well as disease. Quercus robur added, as waif.
Unabridged references: [Cottam, W. P., J. M. Tucker, & F. S. Santamour. 1982. Oak hybridization at the University of Utah. State Arboretum of Utah Publication No. 1. Salt Lake City; Hardin, J. W. 1975. Hybridization and introgression in Quercus alba. Journal of the Arnold Arboretum 56: 336–363; Manos, P. S., Doyle, J. J., & Nixon, K. C. 1999. Phylogeny, biogeography, and processes of molecular differentiation of Quercus subgenus Quercus (Fagaceae). Molec Phylogen Evol 12: 333–349.]

Key to Quercus

1. Acorn cup scales thin, not tubercled, shell hairy to woolly inside, at least at tip; bark dark gray or gray-brown to black

2. Leaf moderately to deeply lobed, lobes 1–4-toothed, teeth generally bristle-tipped; plant deciduous ..... Q. kelloggii

2' Leaf entire to toothed, teeth abruptly pointed to spine-tipped, not bristle-tipped; plant evergreen

3. Leaf generally adaxially convex, margin rolled under or not, obscuring marginal teeth, blade generally widely elliptic to round; fruit mature in year 1 ..... Q. agrifolia

4. Leaf abaxially glabrous to sparsely hairy except vein axils hair-tufted ..... var. agrifolia

4' Leaf abaxially densely tomentose ..... var. oxyadenia

3' Leaf adaxially ± flat, margin not rolled under, blade generally lanceolate to oblong; fruit mature in years 1–2

5. Leaf abaxially ± yellow or ± white woolly; fruit mature in year 1 ..... Q. ilex

5' Leaf abaxially glabrous; fruit mature in year 2

6. Leaf 2–5 cm, abaxially generally ± shiny, yellow-green; nut distally acute to ± obtuse ..... Q. wislizeni

7. Shrub 2–4(6) m ..... var. frutescens

7' Tree generally 10–22 m ..... var. wislizeni

6' Leaf 3–9(14) cm, abaxially generally ± dull; nut distally obtuse to ± rounded ..... Q. parvula

8. Tree < 17 m — s North Coast, Inner North Coast Ranges, Central Western California (except Inner South Coast Ranges), Western Transverse Ranges ..... var. shrevei

8' Shrub 1–6 m

9. Leaf margin generally entire; Outer South Coast Ranges (Santa Barbara Co.), n Channel Islands (Santa Cruz Island), e Western Transverse Ranges ..... var. parvula

9' Leaf margin long-tapered dentate; San Francisco Bay Area (Mount Tamalpais) ..... var. tamalpaisensis

1' Acorn cup scales generally thick, generally tubercled to ± not, shell glabrous to woolly inside; bark light gray to ± white

10. Acorn nut shell ± woolly inside; fruit mature in year 2; plants evergreen

11. Leaf generally 3–8 cm; acorn cup > 1.5 cm wide; generally tree, > 7 m

12. Leaf adaxially with lateral veins ± not impressed, abaxially golden-puberulent, glabrous in age ..... Q. chrysolepis

12' Leaf adaxially with lateral veins impressed, abaxially densely tomentose, sparsely tomentose in age — Channel Islands ..... Q. tomentella

11' Leaf generally 1–3.5 cm; acorn cup < 1.5 cm wide (if > 1.5 cm wide, leaves <= 3 cm); generally shrub, < 7 m

13. Twigs rigid; leaf margin wavy, strongly spine-toothed; blade elliptic to round-ovate; plants 2–6 m, erect ..... Q. palmeri

13' Twigs flexible; leaf margin entire to irregularly serrate, teeth mucronate or spine-tipped; blade oblong or lanceolate to ovate; plants to 5 m, prostrate to erect

14. Leaf margin entire or with few irregular spine-tipped teeth; dry chaparral, 100–1800 m, sw Peninsular Ranges ..... Q. cedrosensis

14' Leaf margin entire to mucro-toothed; montane conifer zone, 900–2800 m, Klamath Ranges, High North Coast Ranges, Inner North Coast Ranges, High Cascade Range, High Sierra Nevada, Modoc Plateau ..... Q. vacciniifolia

10' Acorn nut shell glabrous inside; fruit mature in year 1; plants evergreen or not

15. Leaf lobed (± entire, wavy, or ± lobed in Quercus douglasii), margins generally without spines; plants deciduous

16. Leaf abaxially glabrous (in youth sometimes sparsely hairy), base strongly cordate, often revolute; fr on axillary peduncle (25-)35–65(-100) mm ..... [Q. robur]

16' Leaf abaxially fine-hairy, puberulent, fine-tomentose, short-hairy, or densely appressed-stellate-hairy, base wedge-shaped, rounded-gradually tapered, or truncate (subcordate); fr subsessile or rarely on axillary peduncle to 10(-20) mm

17. Leaf shallowly lobed (sinuses generally < 1/2 distance lobe tip to midrib), adaxially generally dull, green to blue-green

18. Leaf adaxially green; acorn cup scales tubercled; Channel Islands ..... Q. ×macdonaldii

18' Leaf adaxially blue- or gray-green; acorn cup scales ± tubercled; mainland

19. Shrub, tree < 3 m, evergreen to deciduous; leaves 1.5–5 cm, generally irregularly coarsely toothed, adaxially blue- or gray-green ..... Q. ×alvordiana (2)

19' Tree, deciduous; leaves 3–6(8) cm, ± entire, wavy, or ± lobed, adaxially blue-green ..... Q. douglasii

17' Leaf moderately to deeply lobed (sinuses generally > 1/2 distance lobe tip to midrib), adaxially ± shiny, dark green

20. Tree; acorn cup 10–30 mm deep, all scales tubercled; nut 30–50 mm, generally long-conic, distally acute to ± obtuse ..... Q. lobata

20' Shrub to tree; acorn cup 4–9 mm deep, proximal scales ± tubercled, distal ± not; nut 20–30 mm, ovoid to ± spheric, distally rounded ..... Q. garryana

21. Tree 8–20 m, generally with 1 trunk; terminal buds 5–12 mm, fusiform, hairs dense, ± yellow or ± white ..... var. garryana

21' Shrub to small tree 0.3–5 m, generally with > 1 trunk; terminal buds 2–5 mm, hairs sparse, brown or ± red

22. Rays of stellate hairs on leaf abaxially generally 4–6, 0.25–0.5 mm; Klamath Ranges, High North Coast Ranges, Central Coast ..... var. breweri

22' Rays of stellate hairs on leaf abaxially generally 6–8, < 0.3 mm; Klamath Ranges, Inner North Coast Ranges, Cascade Range, Sierra Nevada, San Francisco Bay Area, Outer South Coast Ranges, ne Western Transverse Ranges, Modoc Plateau ..... var. semota

15' Leaf generally entire to toothed, not lobed, teeth with spines or not; plants generally evergreen

23. Leaves 7–11(18) cm, serrate, lateral veins of larger leaves generally 20–28, generally straight and prominent; stipules persistent, > 10 mm, silky-hairy ..... Q. sadleriana

23' Leaves 1–6 cm, entire to dentate, lateral veins of larger leaves generally < 20, generally not straight and prominent; stipules early-deciduous, < 10 mm, not silky-hairy

24. Shrub to tree generally > 5 m; leaves 2–6 cm, oblong to obovate, entire or ± toothed, adaxially shiny green to dull blue-green

25. Shrub, small tree 5–6(10) m; leaf blade (10)20–35(60) mm, adaxially shiny green to dull blue-green, margin entire, dentate, or wavy-dentate ..... Q. ×acutidens (2)

25' Tree 5–25 m; leaf blade (20)30–60(80) mm, adaxially blue-green, dull, margin wavy-dentate to generally entire ..... Q. engelmannii

24' Shrub to small tree generally < 5 m (Quercus berberidifolia sometimes a small tree to 8+ m); leaves 1–5 cm, elliptic to ovate or ± round, variously toothed, adaxially shiny to dull green to dull blue-, yellow-, or gray-green

26. Leaf 2-colored, adaxially yellow- to gray-green, abaxially ± white, densely fine-tomentose, hairs obscuring lateral veins ..... Q. cornelius-mulleri

26' Leaf 1–2-colored, adaxially green to gray- or blue-green, abaxially dull light or pale green or gray-green, not densely tomentose, hairs not obscuring lateral veins

27. Leaf generally oblong to obovate, margin wavy to obtuse-toothed; Peninsular Ranges ..... Q. ×acutidens (2)

27' Leaf elliptic to ovate or ± round, margin toothed, teeth abruptly pointed to spine-tipped

28. Acorn cup thin, scales ± tubercled to not; leaf adaxially gray- or blue-green, dull

29. Acorn stalk 10–15 mm, nut cylindric-ovoid to elliptic, 12–23 mm, generally yellow-brown, distally obtuse; leaves oblong to elliptic, generally regularly spine-toothed ..... Q. turbinella

29' Acorn stalk 0, nut conic-ovoid, 20–40 mm, generally dark brown, distally acute to ± obtuse; leaves oblong to elliptic or obovate, irregularly toothed, teeth blunt to weakly spiny

30. Shrub to small tree < 3 m; leaves 1.5–5 cm, toothed but not spine-toothed, adaxially blue- to gray-green ..... Q. ×alvordiana (2)

30' Shrub 2–5 m to tree < 7 m; leaves 1.3–2.8 cm, spine-toothed, adaxially gray-green ..... Q. john-tuckeri

28' Acorn cup thick, scales tubercled; leaf adaxially generally green, ± shiny (dull or not in Quercus durata)

31. Leaf adaxially dull, convex, margin often rolled under, obscuring teeth ..... Q. durata

32. Leaf adaxially strongly convex, abaxially short-hairy when young; generally on serpentine, North Coast Ranges, n Sierra Nevada, s Central Coast, San Francisco Bay Area, South Coast Ranges ..... var. durata

32' Leaf adaxially ± convex, abaxially densely short-hairy when young; not on serpentine, se Western Transverse Ranges, San Gabriel Mountains (s slope) ..... var. gabrielensis

31' Leaf adaxially ± shiny, flat to ± wavy, not convex, margin generally not rolled under

33. Leaf abaxially with spreading, 2–6-rayed hairs — South Coast, Peninsular Ranges, chaparral or coastal-sage scrub, < 200 m ..... Q. dumosa

33' Leaf abaxially with appressed, 4–10-rayed hairs

34. Leaf base wedge-shaped or generally truncate or rounded; margin mucro- or spine-toothed; widespread on mainland ..... Q. berberidifolia

34' Leaf base gradually tapered, wedge-shaped, or rounded; margin entire, wavy, or ± toothed, teeth generally mucronate; Channel Islands ..... Q. pacifica


Citation for the whole project: Jepson Flora Project (eds.) [year] Jepson eFlora, [accessed on month, day, year]
Citation for an individual treatment: [Author of taxon treatment] [year]. [Taxon name] in Jepson Flora Project (eds.) Jepson eFlora, [URL for treatment]. Accessed on [month, day, year].
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