KEY TO GENERA based primarily on tree leaf characteristics

To use this key effectively become familiar with the leaf characteristics simple and compound, alternate and opposite, and the main types of venation: "Leaf" in Wikipedi.

Adapted from McMinn, Howard E. and Evelyn Maino. 1951. An illustrated manual of Pacific coast trees; with lists of trees recommended for various uses on the Pacific coast by H. W. Shepherd. 2d ed. Berkeley, Calif.: University of California Press.

1. Plant a tree-fern: Cyathea, Dicksonia
1'. Plant not fern-like. Go to choice 2

2. Plants palm-like
2'. Plants not palm-like; leaves arising from branches or branchlets. Go to choice 3

3. Branches passing through compact cylindrical or spherical clusters of sessile capsules and continuing as foliage shoots (illustration)
3'. Branches not as above. Go to choice 4

4. Conifers: leaves typically less than 3/8 inch wide, narrowly lanceolate, linear, needle-like, awl-shaped, or scale-like
4'. Broad-leaf trees: leaves typically more than 3/8 inch wide. Go to choice 5

5. Leaves opposite or some whorled
5'. Leaves alternate

Group 5. Trees with leaves opposite or whorled

N.B. Some ubiquitous opposite-leaved plants not included in the key that are usually seen as sheared hedges but can also attain small-tree form include boxwoods and common myrtle. Also, juvenile leaves of some eucalypts are opposite; see Eucalyptus notes.

1. Leaves compound ... Go to choice 2
1'. Leaves simple ... Go to choice 9

2. Leaves palmately compound ... Aesculus
2'. Leaves pinnately compound ... Go to 3

3. Leaflets 3, coarsely lobed and/or toothed; fruit a 2-winged samara ... Go to choice 4
3'. Leaflets usually 5 or more, toothed or not; fruit various but not a 2-winged samara ... Go to choice 6

4. Leaflets unevenly lobed; reddish tree bark peeling away in paper-thin sheets ... Acer Griseum
4'. Leaflets with coarsely-toothed edges; bark not peeling away in paper-thin sheets ... Go to choice 5

5. Leaflets green ... Acer Negundo
5'. Leaflets with broad white margins and splotches ... Acer Negundo var. variegatum

6. Leaves twice-divided ... Go to 7
6'. Leaves once-divided ... Go to 8

7. Ultimate leaflets sometimes attached by very broad bases ... Lyonothamnus
7'. Ultimate leaflets attached by very short petioles or sessile (no petiole) ... Jacaranda

8. Lflts usually 7 (or 5 to 9), usually unequal (oblique) at base; fruit small, soft berries ... Sambucus
8'. Lflts 5 to 13, usually not unequal at base; fruit a dry, 1-seeded winged samara ... Fraxinus

9. Leaves more than 2.5 inches wide ... Go to 10
9'. Leaves less than 2.5 inches wide ... Go to 12

10. Lvs palmately veined and lobed, the lobes usually toothed; fruit a 2-winged samara ... Acer
10'. Lvs pinnately veined, 5 to 12 inches long, margins entire, fruit a capsule ... Go to 11

11. Lvs sometimes in whorls of 3, with an unpleasant odor when crushed; fruit a slender cylindrical capsule,
 6 to18 inches long ... Catalpa
11'.  Lvs not in whorls of 3, no odor when crushed; fruit an ovoid capsule 1 to 2 inches long  ... Paulownia

12. Lvs toothed or lobed ... Go to 13
12'. Lvs entire, not lobed ... Go to 14

13. Lvs ≤ 3/4 inch wide ... Lyonothamnus
13'. Lvs more than 3/4 inch wide, palmately veined; fruit a 2-winged samara ... Acer

14. Lvs gray- or white-hairy beneath ... Go to 15
14'. Lvs green both surfaces, sometimes distinctly pale green but not dense-hairy beneath ... Go to 19

15. Leaves variously hairy beneath but not felt-like; converging primary or secondary veins smoothly arching toward leaf tip ... Go to 16
15'. Leaves felt-like beneath; secondary veins not like above; ... Go to 17

16. Leaves thin, with secondary (lateral) veins branching from the midvein ... Cornus
16'. Leaves velvet-like, with 5 primary veins from leaf base ... Tibouchina

17. Leaves  1/3 to 2/3 inch wide, flowers in clusters, fruit an olive ... Olea
17'. Leaves wider, secondary veins festooned; flowers solitary or 2-3 together, crowned by persisitent calyx-lobes ... go to 18

18. Flowers single, white outside, purplish inside; somewhat common on campus ... Feijoa sellowiana
18'. Flowers 1, or 2 or 3 together, white; uncommon on campus ... Psidium guajava

19. Leaves with some hairs beneath, thin, lateral veins curve up toward leaf tip; flowers with large. showy white bracts ... Cornus
19'. Leaves mostly smooth beneath, thin to thick-leathery, secondary veins various; flowers without showy white bracts ... Go to 20

20. Lvs 3 to 8 inches long ... Go to 21
20. Lvs 1 to 3 inches long (to 4 inches long for Chionanthus) ... Go to 23

21. Lvs long, narrowly elliptical, mostly less than 1 inch wide, commonly in whorls of three ... Nerium
21'. Lvs ovate to broadly elliptical, more than 1 inch wide ... Go to 22

22. Leaves leathery, paler green below; petioles mostly .25 to .5 inches long ... Go to 23
22''. Leaves membraneous, thin, dark dull green both sides; petioles .5 to .75 inch long ... Syringa

23. Leaves dull above, secondary veins distinct; leaf petioles .5 inches long with distinctive twist ... Chionanthus
23'. Leaves shiny above, secondary veins obscure; petioles straight ... Ligustrum

24. Lvs leathery, evergreen, usually strictly opposite ... Go to 25
24'. Lvs thinner, deciduous, usually both opposite and slightly alternate, i.e., with very short internodes ... Go to 26

25. Branchlets more or less angled or slightly winged; shoots and young foliage tinged with red ... Syzygium
25'. Branchlets not angled or winged; shoots and young foliage not tinged with red  ... Psidium cattleianum

26. Leaves mostly more than 1.5 inches wide, lower surface paler green; leaf petioles .5 inches long with distinctive twist; fruit olive-like; profuse white flower clusters in spring ... Chionanthus
26'. Leaves frequently 1-inch or less wide, both surfaces similar or not; petioles very short, 1/8-inch or less long, straight ... Go to 27

27. Leaves elliptical, at least twice as long as wide, both surfaces similar, shiny green; fruit a 2-inch diam., red to orange berry (pomegranate); flrs red, individual, in early Summer ... Punica
27'. Leaves broadly oval to obovate, less than twice as long as wide, pale green below; fruit a dry capsule; flowers pink or white in clusters, late summer ... Lagerstroemia