Juniperus occidentalis, known as the western juniper, is a shrub or tree native to the western United States, growing in mountains at altitudes of 800–3,000 metres (2,600–9,800 ft) and rarely down to 100 metres (330 ft).
|At Lava Beds National Monument|
|Natural range in dark green (light green is Juniperus grandis)|
Juniperus occidentalis shoots are of moderate thickness among junipers, at 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.
The Sierra juniper, Juniperus grandis, is sometimes treated as a subspecies or variety of J. occidentalis (as J. occidentalis var. australis). The two species are distinguished by range, form, as well as essential oil and genetic evidence.
- Juniperus occidentalis. 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. Exceptionally tall specimens can be found in the John Day area of Oregon well in excess of 26–28 m (85–92 ft) tall where they compete for sunlight among ponderosa pines at the bottom of some deep side canyons. Howerver, on open and barren ground 4–15 m with a bushier growth habit is more common. 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 grandis. 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. The Bennett Juniper in the Stanislaus National Forest of California is considered the oldest and largest example at possibly 3000 years old, with a height of 26 m and a diameter of 3.88 m.
Juniperus occidentalis usually occurs on dry, rocky sites where there is less competition from larger species like ponderosa pine and coast Douglas-fir. In very exposed positions at high altitude, they can assume a krummholz habit, growing low to the ground even when mature with a wide trunk. Hybrids with Juniperus osteosperma are occasionally found.
The cones are an important food for several birds, including American robin, Clark's nutcracker, 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. 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.
- Farjon, A. (2013). "Juniperus occidentalis". The IUCN Red List of Threatened Species. IUCN. 2013: e.T42242A2965783. doi:10.2305/IUCN.UK.2013-1.RLTS.T42242A2965783.en. Retrieved 15 December 2017.
- "Juniperus grandis R.P.Adams". Plants of the World Online. Royal Botanical Gardens Kew. Retrieved 9 July 2019.
- Flora of North America: Juniperus occidentalis
- Adams, R. P., S. Nguyen, J. A. Morris and A. E. Schwarzbach. 2006. Re-examination of the taxonomy of the one-seeded, serrate leaf Juniperus of southwestern United States and northern Mexico (Cupressaceae). Phytologia 88(3):299-310.
- "Conifers.org Australis". Archived from the original on 2006-06-30. Retrieved 2006-08-05. Cite uses deprecated parameter
|Wikimedia Commons has media related to Juniperus occidentalis.|
- Adams, R. P. (2004). Junipers of the World: The genus Juniperus. Trafford Publishing ISBN 1-4120-4250-X
- Chase, J. Smeaton (1911). Cone-bearing Trees of the California Mountains. Chicago: A. C. McClurg & Co. p. 99. LCCN 11004975. OCLC 3477527. LCC QK495.C75 C4, with illustrations by Carl Eytel - Kurut, Gary F. (2009), "Carl Eytel: Southern California Desert Artist", California State Library Foundation, Bulletin No. 95, pp. 17-20 retrieved Nov. 13, 2011