Joshua Tree National Park, San Bernardino Co., CA. 4-23-06. © Joan Avise

California Fan Palm

Washingtonia filifera

The only native palm in the western US, it grows in disjunct desert oases (where there is a continuous supply of underground water), along the San Andreas fault where water is forced to the surface, and in canyons in the Mojave and Colorado Deserts in California, Arizona and Baja California. In Orange County, it is not native but is an occasional escapee from cultivation in riparian scrub and forest and other mesic habitats (Roberts). It lives for 80-90 years, and is commonly used as an ornamental.  Flowering- Feb. - June.

Mature trees are 30 up to 75 ft. tall and 1 to 2 ft. in diameter, with a thick trunk that is not swollen at the base.  Bolsa Chica Wetlands, Huntington Beach, CA. 1-28-12. © Joan Avise

The leaves form rosettes at the top of the trunk and a persistent skirt of old leaves hangs beneath. Bolsa Chica Wetlands, Huntington Beach, CA. 1-28-12. © Joan Avise

Leaf fronds grow in circular fans measuring 3 to 5 ft. in diameter and are palmately divided into 40 to 60 folded segments, often ripped along half the length.  Margins have thread-like fibers.  Petioles and segment bases have hooked spines on the margin.  Bolsa Chica Wetlands, Huntington Beach, CA. 1-28-12. © Joan Avise

The palm provides critical habitat for many wildlife species including Desert Bighorn Sheep, the Hooded Oriole, Gambel's Quail, and a rare bat species (Lasiurus xanthinus).  The skirt provides shelter for many small birds and invertebrates. Coyotes and small mammals assist in seed dispersal by spreading it in their scat.  Birds (cedar waxwings, robins, bluebirds and mockingbirds, hooded orioles) consume the fleshy part of the fruit, generally not the seed, which is too large for their digestive systems.  Native Americans used fan palm oases for village sites.  The Cahuillas set fire to oases to increase fruit production and also planted palm seeds.  The leaves were used for waterproof shelters, food, clothing and baskets.  Other uses

A similar palm,  Washingtonia robusta, (Mexican Fan Palm), native to Baja, Mexico, can reach twice the height with a swollen base and more slender trunk above. It is becoming a serious pest species in the Santa Ana river drainage (Clarke). The genus name honors George Washington, the first president of the United States.  Urbanization and ground water depletion is causing palm oases to retract and disappear creating a threat to this species.  The palm boring beetle (Dinapate wrightii) can kill various species of palms, including this one, but it generally inhabits older trees, and helps keep the palm population young and vibrant (oases). The red palm weevil (Rhynchophorus ferrugineus) is also a threat to this and other palms (Wikipedia).

The bisexual flowers are in long droopy clusters within the crown.  There are 3 sepals, 3 reflexed white petals, 6 stamens, a 3-lobed superior ovary.  Fruits are edible black drupes 1/3 in. in diameter.  A healthy palm can produce 350,000 seeds.