Juniperus occidentalis (Western Juniper and Sierra Juniper) is a shrub or tree native to the western United States, growing in mountains at altitudes of 800-3,000 m (rarely down to 100 m).

The shoots are of moderate thickness among junipers, 1-1.6 mm diameter. The leaves are arranged in opposite decussate pairs or whorls of three; the adult leaves are scale-like, 1-2 mm long (to 5 mm on lead shoots) and 1-1.5 mm broad. The juvenile leaves (on young seedlings only) are needle-like, 5-10 mm long. The cones are berry-like, 5-10 mm in diameter, blue-brown with a whitish waxy bloom, and contain one to three seeds; they are mature in about 18 months. The male cones are 2-4 mm long, and shed their pollen in early spring.

It usually occurs on dry, rocky sites where there is less competition from larger species like Ponderosa Pine and Coast Douglas-fir. Hybrids with Juniperus osteosperma are occasionally found.

The cones are an important food for several birds, including American Robin, Phainopepla and Cedar Waxwing; these digest the fleshy cone scales and disperse the seeds in their droppings. The plants often bear galls caused by the Juniper Tip Midge Oligotrophus betheli (Bibionomorpha: Cecidomyiidae); these are violet-purple fading to brown, 1-2 cm diameter, with dense modified spreading scale-leaves 6-10 mm long and 2-3 mm broad at the base.

There are two varieties, treated as subspecies by some botanists:

• Juniperus occidentalis var. occidentalis Western Juniper. Southeast Washington, eastern and central Oregon, southwest Idaho, northeastern California and extreme northwest Nevada, north of 40° 30' N latitude, east of the Cascade Range. A shrub or small tree 4-15 m tall. Cones 7-10 mm diameter. About 50% of plants are monoecious with both sexes on the same plant, 50% dioecious, producing cones of only one sex.
• Juniperus occidentalis var. australis Sierra Juniper. California and westernmost Nevada, south of 40° 30' N latitude in the Sierra Nevada and San Bernardino Mountains. A medium-sized tree 12-26 m tall with a stout trunk up to 3 m diameter. Cones 5-9 mm diameter. Most plants dioecious, but about 5-10% are monoecious.

References and external links

• Adams, R. P. (2004). Junipers of the World: The genus Juniperus. Trafford Publishing ISBN 1-4120-4250-X
• Gymnosperm Database: Juniperus occidentalis
• Flora of North America: Juniperus occidentalis

Cupressaceae | Trees of California