W. robusta grows to 25 m (82 ft) tall, rarely up to 30 m (98 ft). The leaves have a petiole up to 1 m (3 ft 3 in) long, and a palmate fan of leaflets up to 1 metre (3 ft 3 in) long. The petioles are armed with sharp thorns. The inflorescence is up to 3 m (10 ft) long, with numerous small, pale orange-pink flowers. The fruit is a spherical, blue-black drupe, 6–8 mm (1⁄4–5⁄16 in) diameter; it is edible, though thin-fleshed.[6]
Taxonomy
It is one of two species in the genus Washingtonia. The other is the close relative Washingtonia filifera, which occupies a more northerly distribution. Compared with W. robusta, W. filifera has a thicker trunk and dull green leaves.[7]
This palm is native to the Baja California peninsula and Sonora. On the peninsula, it occurs from the Sierra de La Asamblea and the Baja California desert south into the Vizcaino region and the Sierra de La Giganta, and into the southern cape.[8] In Sonora, it occurs in canyons in the western half of the state, particularly in the palm oases of the Sierra El Aguaje north of Guaymas. It is relatively restricted, and is suspected to be a relict population in Sonora. It has the least number of plants in the palm oases that are shared with two other more numerous species, Brahea brandegeei and Sabal uresana.[7]
Cultivation
Like the closely related Washingtonia filifera (California fan palm), it is grown as an ornamental tree. Although very similar, the Mexican washingtonia has a narrower trunk (which is typically somewhat wider at the base), and grows slightly faster and taller; it is also somewhat less cold hardy than the California fan palm, hardy to about −8 °C (18 °F).
Field research conducted on W. robusta in its native habitat on the Baja California peninsula concluded that its potential longevity may exceed 500 years.[9] Supporting research by Barry Tomlinson and Brett Huggett states that there is "evidence for extreme longevity of metabolically functioning cells of considerable diversity in palm stems."[10] Many of the iconic "sky dusters" of Los Angeles that have survived the chainsaws of progress are documented in photography from the 19th century.
Washingtonia × filibusta is a hybrid of W. robusta and W. filifera, and has intermediate characteristics of the two parents, especially greater tolerance of wet cold.[11]
^Felger, Richard Stephen; Johnson, Matthew Brian; Wilson, Michael Francis (2001). The Trees of Sonora, Mexico. New York, New York: Oxford University Press. p. 391. ISBN0-19-512891-5.
^Little, Elbert L. (1994) [1980]. The Audubon Society Field Guide to North American Trees: Western Region (Chanticleer Press ed.). Knopf. p. 326. ISBN0394507614.
^Tomlinson, P. Barry; Huggett, Brett A. (2012-12-01). "Cell longevity and sustained primary growth in palm stems". American Journal of Botany. 99 (12): 1891–1902. doi:10.3732/ajb.1200089. ISSN0002-9122. PMID23221497.
