California fan palm, desert fan palm
Stems: Solitary, columnar, upright to 15 m tall and 100-150 cm diameter, covered with a skirt of marcescent leaves (unless removed for landscape appeal). Old leaf bases usually fall away after many years, to leave a smooth gray stem with closely spaced leaf scar rings. Leaves: Costapalmate, induplicate, split about half the blade length into numerous segments with pendulous tips and threads (marginal fibers) hanging between segments. Several grayish-green leaves form an open crown. Petioles split, armed with curved teeth. The base of the lower surface of the leaf blade scantly covered with near white pubescence. The adaxial hastula is prominent with tattered margins. Flowers and fruits: Inflorescences are numerous, branched to at least three orders, and project from the crown extending beyond the leaves. Individual flowers are bisexual, white. Fruits are spherical to pear-shaped, up to 1 cm in diameter, and brownish-black to black when ripe.
Field: Solitary, columnar, upright to 15 m tall and 100-150 cm diameter, covered with a skirt of marcescent leaves. Washingtonia filifera has an open crown of grayish green, costapalmate leaves with armed petioles split at the base.
Washingtonia robusta, but that species has a tapered stem, roughly twice as wide at the base as the apex, and bright green leaves forming a dense crown, rather than the columnar stemmed W. filifera, with grayish-green leaves and long petioles forming an open crown.
Native to the southwestern United States (California and Arizona) and Mexico
The two Washingtonia species hybridize freely, making identification of cultivated palms difficult. In Florida, W. robusta is more often planted; in California and Arizona, both are planted, but W. filifera is more common. Both species are planted in drier areas of Hawaii, but W. robusta is much more common.
The fungal disease caused by Sphaerodothis neowashingtoniae, called diamond scale, can infect Washingtonia filifera and its hybrids, leading to loss of leaves and an even sparser crown.
Washingtonia filifera (Linden ex André) H.Wendl. ex de Bary
Neowashingtonia filifera (Linden) Sudw.
Pritchardia filifera Linden ex André
Washingtonia filamentosa (H.Wendl. ex Fenzi) Kuntze
Washingtonia sonorae S.Watson