March 30, 2009

Plant Portraits

David DeardorffLasca Leaves 26:43-45, 1976
It is somehow fitting in this bicentennial year for a plant- portrait article to highlight a species in a distinctive genus of ornamental fan palms named after the “father of our country”. The genus is Washingtonia; it is comprised of just two species: W. filifera, the only palm native to the western United States, and W. robusta.The name Washingtonia was used by Rafinesque in 1818 for sweet cicely, a genus of herbs in the carrot family. Later on it was used by Wendland for the fan palms and was also once used for the sequoias. According to the International Rules of Botanical Nomenclature, no two genera may have the same name, and the oldest validly published name has priority. Since Rafinesque used the name before anyone else, sweet cicely, not the fan palm, should be named Washingtonia. Nearly a hundred years later, however, Parish prepared a taxonomic monograph of the fan palms (Bot. Gaz. 44: 408-434, 1907.). In this study, he decided that the fan palms should retain the name Washingtonia. He made this decision based on what he considered to be sound nomenclatural grounds and also the fact that by this time the use of the name for the palms was solidly entrenched in the literature and in the nursery trade.Washingtonia robusta, the Mexican fan palm, is native to northwestern Mexico and may have been introduced to California as early as the eighteenth century by the mission fathers. It has been noted that Prudhomme grew this palm at his home near San Gabriel and apparently obtained his plants from the mission there. The Mexican fan palm was not extensively planted, however, until around 1870. E. J. Baldwin introduced it in his Rancho Santa Anita in the 1890’s. This planting still exists near the Queen Anne Cottage on the grounds of the Los Angeles State and County Arboretum. Several of these magnificent old palms exceed 100 feet in height and one tops them all at 121 feet. This grand old palm at the northeast corner of the Queen Anne Cottage may well be the tallest palm in the continental United States.Under ideal conditions of good drainage, ample soil moisture, and fertile soil, the Mexican fan palm gains an average of two feet per year in height. At least one record reports a vigorous growth rate of six feet in a single year. It is apparently the ultimate height of the Mexican fan palm which earned it the specific epithet of robusta, since in every other respect it is smaller and more graceful than the relatively massive California fan palm, W. filifera. The smaller leaves, smaller crown, and narrow trunk of the Mexican fan palm result in a graceful habit which is accentuated by the extreme heights it can reach.The leaves of the Mexican fan palm are palmately divided, the divisions extending about one-third of the distance to the base of the blade. The leaves are as much as four feet long, including the stout spiny petiole, and are persistent for several years. The functional life of the leaf is about one year after which it dies and becomes reflexed, dangling down around the trunk in a skirt or petticoat of thatch. The skirts of old leaves persist for years unless pruned away deliberately or removed by wind or fire. When the dead leaves are deliberately pruned, the leaf bases which remain form a very attractive basket-weave texture for much of the length of the trunk.The flowers of the Mexican fan palm are small and whitish, borne in large inflorescences which hang down below the leaves. The fruits are small blue-black drupes with a large seed and very little flesh. The seeds germinate readily and small seedling fan palms often spring up abundantly around reproductively mature trees.The native Americans of the southwest utilized the California fan palm in a variety of ways and, although no specific information seems to be available for the Mexican fan palm in this regard, it may have been used in a similar fashion. The fruits were roasted and eaten or were ground into flour. The trunks were squared off and used as timbers or were split into poles for ramadas and corrals. The leaves provided thatch for roofs and fibers to bind the thatch in place. Thus it may have been for partly utilitarian rather than strictly ornamental purposes that the Mexican fan palm was originally imported by the mission fathers.Whatever the original reasons for its importation, the Mexican fan palm is highly regarded today as a hardy, adaptable, ornamental palm performing well under a wide variety of climatic and cultural conditions. The plants are hardy to 24 degrees and will withstand drought and poor soil, although growth is faster under better conditions. The most widely planted palm in southern California, the Mexican fan palm is now cultivated in Mediterranean and subtropical regions around the world. It is certainly the most abundant tree in the urban landscape of southern California, dominating the skyline of cities and towns from the coast to the desert. It is a stately street tree and, especially when silhouetted against the setting sun, is quite capable of transforming the most mundane urban landscape into a panorama of genuine beauty. Even more than most trees, however, it achieves its true potential when planted in informal clumps and groves in a park-like setting. The magnificent grove of Mexican fan palms near the Queen Anne Cottage on the Arboretum grounds is an excellent example of their quiet grace.Dr. Deardorff is a member of the department research staff involved in taxonomic studies.