Juniperus occidentalis


Juniperus occidentalis

Taxobox
name = "Juniperus occidentalis"
status = LR/lc | status_system = IUCN2.3



image_width = 240px
image_caption = Tree of var. "occidentalis", Lava Beds National Monument
regnum = Plantae
divisio = Pinophyta
classis = Pinopsida
ordo = Pinales
familia = Cupressaceae
genus = "Juniperus"
species = "J. occidentalis"
binomial = "Juniperus occidentalis"
binomial_authority = Hook.

"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. Exceptionally tall specimens can be found in the John Day area of Oregon well in excess of 26-28 m tall (80-90 feet+) competing for sunlight among Ponderosa Pines at the bottom of some deep side canyons, but 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 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.

The Bennett Juniper in the Stanislaus National Forest of California is one of the oldest and largest examples at possibly 3000 years old, with a height of 26 m and a diameter of 3.88 m [http://www.conifers.org/cu/ju/australis.htm] .

References and external links

*
*Adams, R. P. (2004). Junipers of the World: The genus Juniperus. Trafford Publishing ISBN 1-4120-4250-X
* [http://www.conifers.org/cu/ju/occidentalis.htm Gymnosperm Database: "Juniperus occidentalis"]
* [http://www.conifers.org/cu/ju/australis.htm Gymnosperm Database: "Juniperus occidentalis" var. "australis"]
* [http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=233500734 Flora of North America: "Juniperus occidentalis"]


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