This key considers only the gross characters of trees in question which can be readily noted by the layman. It is of the dichotomous type (regularly branching in pairs). Beginning with No. 1 on the left one merely selects the character which fits the tree which is being studied. One is thus referred to the next pair of possibilities by the number noted on the right. Continuing in that manner the observer finally eliminates successive distinguishing characters until the identity of the tree noted is given.

o—o

1. Leaves alternate 2

1. Leaves opposite 14

2. Foliage evergreen 3

2. Foliage deciduous 5

3. Margins of leaves not toothed; leaves with pungent odor when crushed. Fruit green and olive-like California laurel (see page 20)

3. Margin of leaves often toothed and holly-like in appearance; fruit an acorn 4

4. Cup of acorn covered with bright yellow “wool.” Found from 3,000 to 6,000 ft.; common in rocky soils bordering cliffs Canyon live oak (see page 16)

4. Cup of acorn not wooly but scaly; acorn conical. Found up to 2,000 ft.; very rare in park Interior live oak (see page 18)

5. Leaves pinnately compound with from 7 to 19 subopposite rounded leaflets; flowers white, in clusters and pealike; fruit a pod with several seeds; twigs with short spines. An introduced tree Black locust (see page 34)

5. Leaves simple, not compound 6

6. Leaves large and deeply cleft into about seven lobes, each with four bristle-tipped points; fruit an acorn California black oak (see page 14)

6. Leaves not deeply cleft 7

7. Margin of leaves not toothed or sinuately lobed (wavy). Fruit an acorn. Found occasionally up to 2,000 ft.; very rare in park Blue oak (see page 19)

7. Fruit not an acorn and foliage not as described above 8

8. Leaves narrow and elongated Willows (see page 6)

8. Leaves not as noted above 9

9. Leaves more or less triangular in outline; broadest at base and tapering to a point at apex 10

9. Leaves not as noted above; either ovate, oblong, or round in outline 11

10. Leaves large, 2 to 7 inches long, margins finely toothed, thick and leathery in texture, shiny green above and pale green to silvery beneath. Bark heavily ridged and dark gray on large trunks; pale gray on young trees. Common in moist soils up to 4,500 feet Black cottonwood (see page 7)

10. Leaves 1 1/2 to 3 inches long, roundly tapering to a point at the apex; margin of leaf with small teeth; stem or petiole of leaf long and flattened from the side, causing foliage to flutter in slightest breeze. Bark generally smooth and white. Not found below 5,000 feet Quaking aspen (see page 9)

11. Leaves circular or almost so; margin with small teeth. Attractive white flowers approximately one inch in diameter. Fruit (34 to 1 inch long) deep purple-red in color and tart to taste Klamath plum (see page 22)

11. Leaves not circular but ovate (widest below middle) or oblong in outline 12

12. Margin of leaves coarsely toothed; prominent veins extending to leaf margins 13

12. Margin of leaves finely toothed; leaves oblong in outline. White flowers (in spring) borne in compact, elongated clusters. Fruit a blackish berry Western chokecherry (see page 21)

13. Leaves ovate in outline (1 to 2 inches wide, 2 to 3 inches long). Staminate flowers, common in spring, in elongated pendent, tassel-like catkins. Seeds borne in small, distinctive, green (black after maturity) “cones.” Bark steel gray in color and usually smooth. Common along streams White alder (see page 12)

13. Leaves oblong in outline (1 to 3 inches wide, 3 to 5 inches long), doubly toothed on margin, and lopsided at base. Flowers produced in loose clusters before unfolding of leaves. Seeds flat and entirely surrounded by thin, papery wing. Bark dark gray and ridged. An introduced tree American elm (see page 32)

14. Leaves compound 15

14. Leaves not compound 16

15. Leaves palmately compound with five to seven leaflets, each three to seven inches long. Flowers in showy, white, elongated clusters. Fruit a buckeye. Rare in park but common along approach roads to park from San Joaquin Valley California buckeye (see page 27)

15. Leaves pinnately compound. Seeds with elongated wings, borne in bunches. Very rare in park but found along lower parts of western park boundary; will be noted in vicinity of El Portal Oregon ash (see page 29)

16. Leaves “maple-like”, palmately divided into three to five lobes; winged seeds produced in pairs 17

16. Leaves not divided; oblong in outline. Large white blossoms conspicuous in spring; clusters of bright red seeds conspicuous in fall Pacific dogwood (see page 25)

17. Leaves small, one to three inches wide; leaf stems occasionally red; winged seeds rosered before maturity, changing to russet brown, about one inch long. Usually a tall shrub in gravelly to rocky soils in protected locations Rocky Mountain maple (see page 24)

17. Leaves larger than above at maturity. Seeds larger. Flowers yellow-green in color 18

18. Leaves large, sometimes twelve inches wide; fragrant yellow flowers in pendent, compact clusters (racemes). Seeds large, one to one and one-half inches long including the wing. The common maple of this region. Big leaf maple (see page 23)

18. Leaves 1 to 3 inches wide at maturity; yellow-green flowers in loose, open clusters (corymbs). Seeds, including wings, rarely longer than one inch. Uncommon introduced tree Sugar maple (see page 35)

Parts, kinds, arrangements, and venation of leaves

[click to enlarge]

From McMinn and Maino: Pacific Coast Trees. Courtesy of the University of California Press

Parts, kinds, arrangements, and venation of leaves

1. Stem with simple alternate leaf, with netted venation; b, bud; bl, blade; p, petiole; s, stipules. 2. Stem with opposite, palmately veined and lobed leaves. 3. Pinnately compound leaf; 1, leaflet; p, petiole; pt, petiolule; r, rachis. 4. palmately compound leaf. 5. Simple leaf with parallel venation. 6. Fascicled leaves; s, sheath. 7. Steno with whorled leaves. S. Straight-veined leaf.

[click to enlarge]

From McMinn and Maino: Pacific Coast Trees. Courtesy of the University of California Press

Margins of Leaves

1. Entire. 2. Serrate. 3. Dentate. 4. Crenate. 5. Sinuate. 6. Pinnately lobed. 7. Palmately lobed.

[click to enlarge]

From McMinn and Maino: Pacific Coast Trees. Courtesy of the University of California Press

Shapes of Leaves

1. Scale-like. 2. Awl-shaped. 3.Linear. 4. Lanceolate. 5. Oblong, 6. Elliptic. 7. Oval. 8. Orbicular. 9. Ovate. 10. Cordate. 11. Oblanceolate. 12. Obovate.

[click to enlarge]

From McMinn and Maino: Pacific Coast Trees. Courtesy of the University of California Press

Tips and bases of leaves

1. Acuminate. 2. Acute. 3. Obtuse. 4. Truncate. 5. Emarginate. 6. Mucronate. 7. Rounded. 8. Cordate or heart-shaped. 9. Auriculate. 10. Oblique or unequal. 11. Cuneate or wedge-shaped.

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