Washingtonia filifera

Common name

California fan palm, desert fan palm

Description

Stems: Solitary, columnar, upright to 15 m tall and 100-150 cm diameter, covered with a skirt of marcescent marcescent:
remaining attached after becoming old and withered (e.g., aging leaves of Washingtonia palms suggest the common name, “petticoat palm”)
leaves (unless removed for landscape appeal). Old leaf leaf:
in palms -- the leaf blade (which is usually divided into leaflets or leaf segments), the petiole (or leaf stalk) and the sheath (which forms the attachment of the leaf to the stem)
bases usually fall away after many years, to leave a smooth gray stem with closely spaced leaf leaf:
in palms -- the leaf blade (which is usually divided into leaflets or leaf segments), the petiole (or leaf stalk) and the sheath (which forms the attachment of the leaf to the stem)
scar rings. Leaves: Costapalmate, induplicate,induplicate:
Most palm leaflets or leaf segments are obviously folded. If the folds create a V-shape, with the midrib lower than the margins (so that rain might fall "into a valley"), the folding is 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 leaf:
in palms -- the leaf blade (which is usually divided into leaflets or leaf segments), the petiole (or leaf stalk) and the sheath (which forms the attachment of the leaf to the stem)
blade scantly covered with near white pubescence. The adaxial adaxial:
toward the axis or the side of an organ facing toward the axis (ad as in adhere); for example, the upper surface of a leaf blade or petiole
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.

Diagnostic features

Field: Solitary, columnar, upright to 15 m tall and 100-150 cm diameter, covered with a skirt of marcescent marcescent:
remaining attached after becoming old and withered (e.g., aging leaves of Washingtonia palms suggest the common name, “petticoat palm”)
leaves. Washingtonia filifera has an open crown of grayish green, costapalmate costapalmate:
a fan-shaped leaf with a midrib (costa) extending into the blade, sometimes extending far enough into the blade to cause it to curve (e.g., Sabal palmetto)
leaves with armed petioles split at the base.

May be confused with

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.

Distribution

Native to the southwestern United States (California and Arizona) and Mexico

Additional comments

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.

Scientific name

Washingtonia filifera (Linden ex André) H.Wendl. ex de Bary

Family

Arecaceae/Palmae

Synonyms

Neowashingtonia filifera (Linden) Sudw.

Pritchardia filifera Linden ex André

Washingtonia filamentosa (H.Wendl. ex Fenzi) Kuntze

Washingtonia sonorae S.Watson