A. Seeds produced in cones or berries

B. Female cones woody; leaves needle-like

C. Needles one per fascicle

Pinus monophylla

CC. Needles more than one per fascicle

D. Needles two per fascicle

Pinus murrayana

DD. Needles more than two per fascicle

E. Needles three per fascicle

F. Inner surface of bark pink to brown, vanilla odor

Pinus jeffreyi

FF. Inner surface of bark yellow, resinous odor

Pinus ponderosa

EE. Needles five per fascicle

F. Cones with slender, incurved prickles; eedles with bristle-like appearance on branchlets

Pinus longaeva

FF. Cones unarmed, needles in dense tufts at end of branchlets

Pinus flexilis

BB. Female cones berries; leaves flattened, ternate

C. Bark gray-brown, weathering ash white; leaves with hidden glands; berries with sweet, dry pulp

Juniperus osteosperma

CC. Bark shreddy, reddish to brown; leaves with conspicuous glands; berries with resinous pulp

Juniperus occidentalis

AA. Seeds not produced in cones or berries, but in ripened ovaries

B. Carpellate (female) flowers with a true perianth

Ailanthus altissima

BB. Carpellate (female) flowers without an apparent perianth

C. Leaves pinnately compound; fruit a samara

Acer negundo ssp. californicum

CC. Leaves simple

D. Flowers in fascicles; fruit a samara

E. Leaves palmately lobed

Acer glabrum var. diffusum

EE. Leaves simply or doubly serrate

Ulmus carpinifolia

DD. Flowers borne in catkins; fruit a nutlet or capsule

E. Trees monoecious

Betula occidentalis

EE. Trees dioecious

F. Leaves ovate lanceolate to deltoid, stamens six or more, buds with many scales

G. Petioles flattened or laterally compressed

H. Leaves yellowish green, alike on both sides, coarsely crenate-dentate

Populus fremontii

HH. Leaves green above, paler beneath, crenate or serrulate to almost entire

Populus tremuloides

GG. Petioles terete

H. Leaves dark green above, paler and glaucous beneath, finely serrate; common

Populus trichocarpa

HH. Leaves light green on both surfaces, glabrous, coarsely serrate; rare

Populus angustifolia

FF. Leaves lanceolate to oblanceolate, stamens two to six buds with a single scale

G. Mature leaves glabrous or glaucous beneath

H. Leaves entire or nearly entire

I. Leaves 0.6–1.6 in (1.5–4 cm) wide, yellowish green above

Salix lutea

II. Leaves 0.4–0.8 in (1–2 cm) wide, dark green above

Salix lasiolepis

HH. Leaves serrulate to glandular serrulate

I. Catkin scales dark brown

Salix pseudocordata

II. Catkins scales yellow

J. Stamens two, twigs yellowish to brownish

Salix lutea

JJ. Stamens four to six twigs reddish to brownish

K. Leaves dark green and shiny above

Salix lasiandra

KK. Leaves light green above, paler beneath

Salix laevigata

GG. Mature leaves pubescent or hairy beneath

H. Leaves linear, less than 0.4 in (1 cm) wide

Salix exigua

HH. Leaves oblanceolate to elliptic-oblong, 0.2–0.8 in (0.6–2 cm) wide

I. Capsules glabrous

Salix lasiolepis

II. Capsules pubescent to minutely pubescent

J. Scales yellow with reddish tips

Salix geyeriana

JJ. Scales dark brown

Salix orestera