Washingtonia filifera

Washingtonia filifera (Desert Fan Palm, American Cotton palm, Arizona Fan Palm, or California Fan Palm) is a species of palm tree native to the desert oases of Arizona, southern Nevada, the inland deserts of southern California, and northwest Mexico in Baja California.

Description
It is a tree, growing up to 18 m (60 ft), and exceptionally 25 m, in good growing conditions. The leaves have a petiole reaching up to 2 m long, bearing a fan of leaflets 1½-2 m long with white, thread-like fibers between the segments. When the leaves die, they bend downwards and form a "skirt" around the plant's trunk. This "skirt" provides a home for many invertebrates.

It has pale, red-brown bark. The flowers are white or yellow, emerging on stalks. When these mature, they become black spherical berries up to 5 in (12½ cm) long wide, containing small red seeds.

Ecology
Fan palms provide habitats for a number of animals, particularly the Bighorn Sheep, Hooded Oriole, Gambel's Quail, Coyotes, and a palm boring beetle, Dinapate wrightii. Another animal that is provided a habitat from the fan palm is a rare bat species, Lasiurus xanthinus. Hooded Orioles rely on the tree for food and places to build nests. Both Hooded Orioles and coyotes play a major role in the seed distribution of the fan palm.

Dinapate beetles can be a problem to the trees by chewing through their trunks. Eventually, a continued infestation of the beetles can kill a palm, opening space for a new palm to grow.

Today, urbanization has caused palm oases to disappear. An increase in agriculture has lowered ground water supplies, which decreases the amount of water available at the oases. This creates a threat not only to Washingtonia filifera, but also the organisms that rely on the trees to survive. Joshua Tree National Park preserves and protects healthy examples of the fan palm in the Little San Bernardino Mountains and where water surfaces up from the San Andreas Fault beside Coachella Valley.

Fossils of Washingtonia filifera are known to exist as far north as Colorado, Oregon, and Wyoming. It apparently reached its current form from 50-70 million years.

Grazing animals such as deer and cattle, and in more ancient times, Giant Sloths and other extinct herbivores, can kill the plants through trampling, or or by eating the terminus at the apical meristem, which is the place the plant grows.

This may have kept Washingtonia filifera restricted to a lesser range than would have been expected if one only considers the availability of water sources. Typically, the oasis environment is one that may have been protected from colder climatic changes over the course of evolution. Thus, the fan palm is restricted by water and climate to widely separated relict groves. The trees in these groves show little, if any genetic differentiation, which suggests that Washingtonia filifera is genetically very stable.

Native American use
The fruit of the fan palm was used by Native Americans as food. It was eaten raw, cooked, or ground into flour to use in cakes. The Cahuilla tribes of California used the leaves in making sandals, thatch roofs, and baskets. Its stems were also used to make utensils for cooking. The Moapa Paiutes as well as Southern Paiutes have stated memories of grandparents also using the palm's seeds, fruit, or leaves for various purposes. The Southern Paiutes and the Cahuilla are related linguistically and by ancient trade routes.

Cultivation
Washingtonia filifera is often cultivated as an ornamental tree, though it is not as widely cultivated as Washingtonia robusta, a close cousin of W. filifera. It is one of the hardiest of Coryphoideae palms, and can repeatedly survive dips into the teens and even in several inches of snow, making it a favorite of cold-hardy palm enthusiasts.

They grow best in warm, temperate climates, with dry summers and wetter winters. Specimens outside of Mediterranean climates do not grow very large, rarely exceeding 15 m. They are tolerant of considerable frost and is rated as hardy to USDA zone 8; it will survive temperatures of -10 °C with minor damage, and established plants have survived short, quick periods of temperatures as low as -12 °C, but with severe damage to its foliage.

Etymology
Its genus name, Washingtonia is named after Washington D.C. or George Washington. The species epithet, filifera, is Latin for "thread-bearing", referring to the thread-like fibers between the leaf segments.