Washingtonia filifera is a species of flowering plant in the palm family Arecaceae, native to southwestern North America. Growing to 15–20 m tall by 3–6 m broad, it is technically an evergreen monocot (not actually a tree). Other common names include desert fan palm, California palm, fanpalm, petticoat palm, cotton palm, Arizona fan palm. The specific epithet filifera means "thread-bearing". As an ornamental tree it is cultivated in suitable temperate climates worldwide. Washingtonia filifera grows to 18 metres in height (occasionally to 25 metres) in ideal conditions. The fronds are up to 3.5–4 metres long, made up of a petiole up to 2 metres long, bearing a fan of leaflets 1.5–2 metres long. They have long thread-like white fibers and the petiole are pure green with yellow edges and filifera-filaments, between the segments. The trunk is gray and tan and the leaves are gray green. The shelter that the skirt creates provides a microhabitat for many small birds and invertebrates. Washingtonia filifera can live from 80 to 250 years or more.

The fruit of the fan palm was eaten raw, cooked, or ground into flour for cakes. The Cahuilla and related tribes used the leaves to make sandals, thatch roofs, and baskets. The stems were used to make cooking utensils. Washingtonia filifera is widely cultivated as an ornamental tree. It will survive temperatures of -10 °C with minor damage, and established plants have survived, with severe leaf damage, brief periods as low as -12 °C. The plants grow best in warm temperate climates with dry summers and wetter winters. Specimens outside of Mediterranean climates rarely exceed 15 metres.