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Nihoa Pritchardia
Pritchardia remota
California Fan Palm
Washingtonia filifera
  (Linden ex André) H. Wendl.
Mexican Fan Palm
Washingtonia robusta
  Owner:   C. Michael Hogan    

California Fan Palm along the main wash of Mountain Palm Canyon, Anza Borrego SP
California Fan Palm
Washingtonia filifera

C. Michael Hogan PhD
January 5, 2009

The California Fan Palm is the only palm species native to the continental USA that occurs west of the Balcones Fault Zone of Texas. Surprisingly little genetic variation exists, considering the palm groves are widely disjunctive. Prehistorically this plant was quite important in sustaining Native American peoples in the southwestern USA. The species occurs chiefly in oasis settings, which also harbor unusually rich and diverse desert wildlife.



DISTRIBUTION
California Fan Palm oasis within Mountain Palm Canyon, Anza Borrego SP
The California Fan Palm is found in disjunctive groves with a southern range boundary of the Sierra San Pedro Mártir, Sierra de Juarez, and Sierra Pinta Mountains of Baja California. The northern extent is demarcated by the Cottonwood and Turtle Mountains as well as the community of Twenty-nine Palms, California; furthermore, in the Salton Sea basin the northern range boundary is defined by the hot southern slopes of the Salton basin, where the northern range of Bursera microphylla is also delimited. Five groves have been mapped in La Paz and Yavapai Counties, Arizona, and four other groves are found in Clark County, Nevada. The principal U.S stands occur in the Sonoran Desert, at locations with surface water concentrations associated with the San Andreas Fault. Coastal groves are found only in Mexico: for example at Guaymas.

Each of the known groves of W. filifera within California has been accurately mapped. The local habitat of most groves is at lower reaches of desert washes such as at Mountain Palm Canyon in Anza Borrego, but not typically on the desert floor itself, since peak sustained flow of most desert streams is characteristically at a point somewhat higher in elevation than the ultimate point of discharge, since average or low flow regimes normally dissipate in the desert sands and do not reach the ultimate high flow discharge location. Fossil evidence reveals a prehistoric range extending to Wyoming and Colorado circa 70 million years before present.
Crown of the California Fan Palm



MORPHOLOGY
This tree typically attains a height of 10 to 25 meters and may have a lifespan of around two centuries. Robust leaf petioles may reach 200 cm in length, with a leaflet extent of similar measure. Mature petioles are armed with curved thorns. Margins of mature leaves manifest white, thread-like fibers. Dead leaves fall downwards, remaining appended to the trunk and producing a circumscribing "skirt". This evergreen monocot has a columnar trunk which is often conspicuously bulbous, not unlike the shape of the Chilean Wine Palm, (Hogan) and up to 80 cm in diameter. Mature pygmy forms are found which attain only the minimum 10 m height, but whose girth may approximate 100 cm. The crown presents a rosette of fronds, with lower parts of the trunk absent of living foliage. The exterior bark consists of a thick rind, while the plant's inflorescense exhibits a spadix form. Bisexual blossoms are yellow and white The spherical to ovoid fruits are hung as massive clusters of relatively small blackish red drupes, of characteristic diameter 12 mm; each drupe exhibits a single large seed. Root structures are typically shallow, especially in oasis areas or washes with plentiful water.



ECOLOGY
Trunk base of the California Fan Palm
The principal plant associations as described by the Kuchler system are Saltbush/greasewood, Mesquite bosque, Creosote, Creosote/ bursage and Paloverde/cactus scrub. The Creosote associations are found on lower slopes where seasonal flow in the washes is dying out on the more level desert floors. Mesquite bosque is often associated with closed canopy versions of the palm grove.

A number of faunal species utilize the habitat created by W. filifera. The snake Elaphe rosalica utilizes the skirt of dead leaves for cover In hydric zones amphibians such as the Pacific and Canyon tree frogs take cover under boulders beneath palms. Birds are drawn to W. filifera oases for the abundant palm fruit as well as nesting sites and surface waters at the groves. Hooded orioles eat the fruit and use leaf fibers from older palm leaves as nesting fabric and frequently create their nests within the California Fan Palm. Gray Fox and Coyote consume the fallen fruit of this palm autumnally, when animal prey are less abundant. The bird consumers as well as fox and coyote are important seed dispersers for this palm. Desert Bighorn Sheep also enjoy habitat afforded by the oases for watering and shelter. The Bighorn Sheep sightings made by me and reported by rangers were typically on slopes above palm oases.

The bat Lasiurus xanthinus is attracted to habitat formed by W. filifera; moreover, the boring beetle Dinapate wrightii utilizes the palm trunk, but severe infestations can result in tree death. Additionally the paper wasp as well as several species of scorpions (Phillips) use the leaves as nesting area.



HISTORY
Some First Peoples such as Kamia and Cahuilla often sited their villages at the palm oases for shelter and the valuable plant products. The Mara Oasis, for example, was settled by the Serrano Indians, whilst Cottonwood Springs Oasis in Joshua Tree was a village of the Cahuilla, who left rich archaeological traces of their culture including bedrock mortars and ollas. Many Native Americans consumed fruit of the W. filifera, (Anderson) either raw or ground into flour. The Moapa band of Paiutes as well as other Southern Paiutes employed this palm species for food and materials. It is not surprising that this was a preferred food source of Native Americans, since it is high in nutritional value, particularly with respect to carotene, whose levels in the palm fruit are typically in the range of 180 mg/gm. Cahuilla people used palm leaves for basketry, sandals and thatch roofing. Some tribes used the long flexible petioles for hunting bows. The species itself was named for President George Washington.



CONSERVATION
Approximately 25,000 species members exist at present, distributed among 116 separate, but genetically indistinct populations. W. filifera is damaged by alteration of the water table.(Vogl) This species as a whole is considered vulnerable (Johnson) due to declining populations and ongoing pressure from human overpopulation and consequent agricultural overdrafting of groundwater.

As a case study, the town of Twenty Nine Palms has been overdrafting groundwater, with a resultant three meter decline in the water table at the Mara Oasis within the Joshua Tree National Monument. Competition for water by other phreatophytes and invasives exacerbate the plight of W. filifera. For example, Tamarix ramosissima is known to be such a thirsty competitor. I observed long riparian stretches of this invasive along the lower New River in Imperial County, where extensive human intrusion to the floodplain has been made to promote agricultural expansion. This large shrub has displaced significant native vegetation, likely including certain W. filifera in the last two centuries.


REFERENCES
* C. Michael Hogan. 2008. Chilean Wine Palm: Jubaea chilensis, GlobalTwitcher.com, ed. Nicklas Stromberg
* Steven J. Phillips and Patricia Wentworth Comus. 1999. A Natural History of the Sonoran Desert, Arizona-Sonora Desert Museum, University of California Press, 628 pages ISBN 0520219805
* M. Kat Anderson. 2006. Tending the Wild: Native American Knowledge and the Management of Californias Natural Resources'', University of California Press, 555 pages ISBN 0520248511
* Richard J. Vogl and Lawrence T. McHargue. 1966. Vegetation of California fan palm oases on the San Andreas Fault. Ecology. 47(4): 532-540.
* D. Johnson. 1998. Washingtonia filifera assessment in IUCN Redlist


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