Washingtonia robusta

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Washingtonia
(Washing-tohn-EE-ah)
robusta (roh-BOOS-tah)
Wr1377.jpg
Fairchild Tropical Botanic Garden, Florida. Photo by Dr. Carl E. Lewis/Palmweb.
Scientific Classification
Genus: Washingtonia
(Washing-tohn-EE-ah)
Species:
robusta (roh-BOOS-tah)
Synonyms
None set.
Native Continent
America
America.gif
Morphology
Habit: Solitary
Leaf type: Palmate
Culture
Survivability index
Common names
Mexican Fan Palm.

Habitat and Distribution

Washingtonia robusta is found in California, Florida, Hawaii, Mexico Northwest,
Menton, French Côte d'Azur, France. Photo by Philippe
La Réunion Island, and Spain. This palm is native to the desert mountain valleys and canyons of Sonora and Baja Mexico. It is a popular landscape plant in Florida, California and Arizona and in areas where it is hardy throughout the world.

Description

Soaring to over 100 ft (30.5 m), this skyscraper of the palm world is a striking sight when planted at equal intervals along a boulevard or when snuggled up in groups against high rise buildings. The gray trunk is ringed with closely set leaf scars although usually at least part of the trunk remains covered with dead leaves that hang in a thatch. The solitary trunk, about 10-12 in (25.4-30.5 cm) in diameter, bulges at the ground and becomes slender as it approaches a crown of large palmate leaves with gracefully drooping leaflet tips. These are rich glossy green and grow to about 5 ft (1.5 m) long and 4 ft (1.2 m) wide. They are borne on 3 ft (0.9 m) orange leaf stems that are edged with vicious saw-tooth spines. As the leaves die, they fall against the trunk to create the "hula skirt" effect for which this palm is famous. Unfortunately this shaggy skirt of dead dry leaves is a fire hazard and provides a home for rats and other undesirable creatures. Many municipalities in California require that the dead leaves be removed which can be quite a hassle when they're dangling 80 ft (25 m) up in the air! In Florida this is not such a problem as the humid climate and occasional high winds tend to keep the palms skirt-free. Washington palms in Florida usually do not reach maximum height, tending to get their crowns blasted off by lightning when they begin to tower over neighboring trees. (Floradata.com) Editing by edric.

Culture

Washington palm prefers a moderately rich well drained soil but can survive on poor soils, even sand. Light: It does best in bright sunny conditions but Washington palm will tolerate some shade. Moisture: Washington palm is drought resistant when established, but looks better and grows faster when given adequate moisture. Hardiness: USDA Zone: 9a. Washington palm is hardy down to about 20º F. but foliage will be damaged at that temperature. Propagation: Propagate by seeds, which will germinate within 2 months. (botanyboy.org)

Frond removal must be done carefully to protect the health of the tree. It is common practice to over prune them, leaving just a few fronds in the crown. While this rarely kills the tree, it can become a problem if done on a regular basis, since the tree may not be able to photosynthesize enough to provide adequate nutrition to the crown and adjoining trunk. Trees that are pruned this way again and again can lose vigor and the upper trunk can become spindly such that the crown dies or breaks off in a high wind. Therefore, it is necessary to leave at least 50% of the green fronds intact. The petiole bases can either be removed or left on, but ultimately they too will fall, creating a mess around the tree and are a potential hazard during high winds. For these reasons it is necessary to remove dead fronds in urban settings or if trees are planted near residences. Municipalities spend a lot of money on cleaning and maintaining street specimens, one reason why this tree is becoming less used in urban settings, especially southern California. The reverse is true here in Japan however – each year I see more and more of them being planted along streets, in parks, and next to apartment buildings. (Floradata.com)

The Mexican fan palm is fairly cold hardy, especially in drier climates. Common estimates rate this palm to at least -6.5 C (20 F) with frond damage occurring several degrees higher, depending on relative humidity and soil moisture (the drier, the more cold resistant). In general W. robusta is more suited to moister climates while W. filifera is a true desert species that is more resistant to cold snaps provided conditions are dry (continuously wet cold conditions can be the death of it however). It is thought that the artificial hybrid of the two, known as Washingtonia “filibusta”, should grow fairly well in cooler climates with wet winters, combining the moisture resistance of W. robusta and the cold hardiness of W. filifera. Areas such as coastal Oregon and Washington states might be good places to try this hybrid, but don’t expect too much cold resistance. (botanyboy.org)

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Comments and Curiosities

This tendency to form a skirt in W. robusta is more typical in younger specimens, but once they attain some height they begin to shed old fronds within a couple years of dying. W. filifera by comparison tends to keep its skirt unless cleaned of old fronds (and the petiole bases). These skirts can attain formidable volumes and are host to all kinds of wildlife – birds, snakes, rodents, insects – you name it. This “petticoat” is also a fire hazard. (botanyboy.org)


External Links

References

Phonetic spelling of Latin names by edric.

Special thanks to Geoff Stein, (Palmbob) for his hundreds of photos.

Special thanks to palmweb.org, Dr. John Dransfield, Dr. Bill Baker & team, for their volumes of information and photos.

Glossary of Palm Terms; Based on the glossary in Dransfield, J., N.W. Uhl, C.B. Asmussen-Lange, W.J. Baker, M.M. Harley & C.E. Lewis. 2008. Genera Palmarum - Evolution and Classification of the Palms. Royal Botanic Gardens, Kew. All images copyright of the artists and photographers (see images for credits).


Many Special Thanks to Ed Vaile for his long hours of tireless editing and numerous contributions.

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