Botany

Leather Oak

Content Cover Image

Leather oak acorn and leaves. Source: Mark S. Brunell

caption Leather oak at The Cedars, Sonoma Co. California. Source: C.Michael Hogan

Quercus durata Jeps. (1909)

The Leather Oak, a California endemic, occurs primarily in the California interior chaparral and woodlands ecoregion. It is a species with strong affinity for ultramafic soils, a geochemical class of high magnesium, low calcium and nutrient deficient media.  In appearance this is a shrub-like tree whose leathery leaves reveal its common name and obvious membership in the sclerophyll vegetation category, a morphological class of hard leaved species that may occur in such diverse places as Australia, Southern Africa, the Chilean matorral and the Mediterranean Basin as well as the California Floristic Province. 

Varieties

Q durata has two recognized varieties: 

  * var. durata, occurs at elevation 150 to 1500 m in the California North and South Coast Ranges, San Francisco Bay Area and northern Sierra Nevada foothills. Upper leaf sufaces of this variety are severely convex
  * var. gabrielensis occurs at elevation 450 to 1000 meters as a limited distribution taxon in the San Gabriel Mountains within San Bernardino and Los Angeles Counties

Morphology

Q. durata manifests as an evergreen shrub typically ranging from 100 to 300 cm in height at maturity, (Jepson)  although it can not uncommonly reach 600 cm in height in circumstances where no burn has occurred for 30 to 50 years. Yellowish or gray twigs are generally tomentose, and the convex oval to elliptic leaves have spiny apexes and enrolled toothed margins. These leaves typically measure 1.5 to 3.0 cm and are dull puberulent above and short hairy pale green below; leaf petioles are approximately one to five mm; secondary leaf veins are conspicuous. The ovoid to cylindric nuts are 1.5 to 2.5 cm in size. The acorn cap is turbinate in shape and covers approximately one third to one half of the nut.

caption Typical habitat of the Leather oak, the Cedars,
Sonoma Co. Calif. Source: C.Michael Hogan

Plant associations and distribution

Q. durata is considered highly tolerant of ultramafic soils, (Kruckeberg) those that are high in magnesium and low in calcium and also characteristically high in nickel and chromium content. These soils are often reddish soils are also typically nutrient poor. (Biedleman and Kozloff) Raiche has correctly pointed out that the botanical literature on Q. durata overstates the species reliance on ultramafic substrates, when, in fact, this oak is found on a variety of volcanic and other non-serpentine soils within the California Floristic Province. (Raiche. 2010)
 
Q  durata is the dominant shrub in Sargent Cypress (Hesperocyparis sargentii) woodlands, which occur in coastal portions of Mendocino, Sonoma, San Mateo, Santa Clara, Monterey, San Benito, San Luis Obispo and Santa Barbara Counties as well as portions of the San Francisco Bay region. The Cedars in Sonoma County is an example of a Sargent Cypress coastal site. In more protected inland locales this woodland type may extend into a riparian zone where summer fogs persist. (Barbour et al.) Grey Pine (Pinus sabiniana) may occur with Sargent Cypress in northern California, while Coulter Pine (P. coulteri) is a common associate in central and southern California. MacNab Cypress (Hesperocyparis macnabiana) woodlands are a somewhat less common ultramafic plant association where the Leather Oak may be a dominant shrub.

Ultramafic chaparral is another common plant community that is found below elevation 500 meters from Santa Barbara County north through the North Coast Ranges and also within the foothills of the Sierra Nevada and portions of the California Central Valley. Here co-dominant shrubs are Chamise (Adenostoma fasciculatum), Coffeeberry (Frangula californica), Interior Silktassel (Garrya congdonii). Buckthorn (Rhamnus crocea) and Toyon (Heteromeles arbutifolia). Scattered taller occurrences of California Bay Laurel (Umbellularia californica), Canyon Live Oak (Quercus chrysolepis) and Coast Live Oak (Q agrifolia) are also found here.  

Q durata is found outside of serpentine environments (Alexander) such as within the Vaca Mountains of Solano and Napa Counties or Hale Ridge of Lake County. In these cases Leather oaks typically occur as isolated individuals within a backdrop of plant associations dominated by California Scrub Oak (Quercus berberidifolia) and Interior Live Oak (Q. wislizeni).

In the case of Q durata gabrielensis, this variety is commonly found in association with California Ash (Fraxinus dipetala), Chaparral Honeysuckle (Lonicera interrupta), Indian Warrior (Pedicularis densiflora), Silver Puffs (Uropappus lindleyi), Sand Fringepod (Thysanocarpus curvipes), Pinon Wormwood (Artemisia dracunculus) and Succulent Lupine (Lupinus succulentus)

Ecology

Q. durata and a number of other California oaks have difficulty in re-establishing stands after forest clearing or in colonization of grassland at a chaparral-prairie boundary. This difficulty is not due to germination rates, but rather relates to the harsh environment of high solar insolation, summer aridity and herbivory in the grassland environment, based upon controlled studies at Jasper Ridge and other sites. (Williams et al.)

Q durata is sometimes afflicted by rust fungi of the genus cronartium.(Amer. Phytopathological Soc.)  The Leather Oak is a host to other parasitic species such as Cynips washingtonensis, who construct spherical galls on Q durata as well as Valley Oak (Q lobata) and Coastal Sage Scrub Oak (Q dumosa). These young galls appear in early spring and can be quite numerously attached to twigs; this gall is typically engulfed in a mass of velvety hairs. The parasite Andricus crystallinus forms irregularly shaped pallidasal galls that agglomerate into masses on the leaves of Q durata, with individual galls being approximately eight to nine mm in length. The gall wasp Neuroterus saltarorius forms a small one millimeter subspherical gall on the Q durata leaf as documented in collected specimens from Brentwood, Marysville and Stockton, California.

Human use

Native American peoples utilized the Leather Oak as a source of food and medicine.After tannins were leached from the acorns, the resulting product was mashed and made into a nutritious mush, which in concert with other oak species was a culinary staple; one of the chief leaching methods was to place raw acorns in a cloth bag and leave this assembly in a stream for several weeks. Certain of the galls found on Q. durata galls are quite astringent, and their extracts were used by California tribes for treatment of dysentery, hemorrhage and diarrhea.

In modern times the leaf mulch from the Leather Oak is applied to gardens for its efficacy in repelling slugs and grubs. After pupation the gall extracts are utilized for tannins and dyes. (Grieve) Modern day uses also include a coffee product and a thickener for soups and stews.

References

  • Jepson Manual. 1993. Quercus durata, University of California, Berkeley
  • Linda H. Biedleman and Eugene N. Kozloff. 2003. Plants of the San Francisco Bay Region: Mendocino to Monterey, 503 pages
  • Arthur R. Kruckeberg. 2004. Geology and plant life: the effects of landforms and rock types on plants,  page 194
  • Michael G. Barbour, Todd Keeler-Wolf, Allan A. Schoenherr. 2007. Terrestrial vegetation of California. page 95
  • Earl B. Alexander. 2007. Serpentine geoecology of western North America: geology, soils, and vegetation, 512 pages
  • Roger Raiche. 2010. personal communication
  • Kimberlyn Williams, Stephen D. Davis, Barbara L. Gartner and Steffan Karlsson, Factors Limiting the Establishment of a Chaparral Oak, Quercus durata Jeps., in Grassland, Symposium on Oak Woodlands and Hardwood Rangeland Management, Oct 31, 1990, Davis, California
  • American Phytopathological Society. 1916.  Phytopathology, Volume 6, page 229
  • M. Grieve. 1984. A Modern Herbal. Penguin Books, Middlesex, England ISBN 014-046-440-9
Glossary

Citation

Hogan, C. (2014). Leather Oak. Retrieved from http://www.eoearth.org/view/article/51cbee547896bb431f697090

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