In their most familiar form, hazelnuts, or filberts, are marble-sized nuts produced primarily from two European species, Corylus avellana and C . maxima. Hazelnuts are believed to be native to Asia Minor, from whence they spread to Italy, Spain, France, and Germany via Greece. They have been cultivated in China for more than 5,000 years. Most commercial hazelnuts today are cultivated in various parts of the world, particularly Turkey, Italy, Spain, China, and the United States. Prior to the 1940s, hazelnuts were exclusively imported, but now Oregon grows about 95% of the filberts consumed in the United States.
Hazelnuts have long been recognized as an excellent source of concentrated protein and they are widely used in desserts and pastries. Recently, they have been found to be an excellent source of fiber, antioxidants, phytoestrogens, and monounsaturated fat (the good fat). Hazelnuts are the richest nut source of folic acid (folate), and they also contain niacin, vitamin B6, vitamin E, potassium, and calcium, as well as the micro-nutrients magnesium, copper, zinc, selenium, and phosphorus.
The common name, hazelnut, is believed to come from the Anglo-Saxon word haesel meaning a headdress or bonnet, referring to the shape of outer shell covering. The derivation of the Latin name corylus, which means hazel tree, is from the Greek word korus, meaning helmet, referring to the shape and hardness of the nut shell. One source of the English common name filbert is St. Philibert’s Day, which occurs on August 20, more or less corresponding to the season in which the nuts ripen. Another possible source of the name is an anglicized German word vollbart, meaning full beard and referring to the appearance of the husked shell. Hazelnut is not related to the astringent, witch hazel, which is derived from the shrub Hamamelis, a member of the sweet gum family Hamamelidaceae, which includes Liquidambar.
The genus Corylus belongs to the birch family (Betulaceae), which includes the birches (Betula) and alders (Alnus). A closely related family, Fagaceae, includes the oaks (Quercus), beeches (Fagus and Nothofagus), and sweet chestnuts (Castanea). There are about 15 species in the genus Corylus, occurring throughout the north temperate regions of North America, Europe, and Asia. There are only two species native to North America, American hazel (Corylus americana) and beaked hazel (C. cornuta), which includes two subspecies, California hazel (C. c. ssp. californica), and beaked hazel (C. c. ssp. cornuta). California hazel is most often treated as a variety of the northern C. cornuta, as it is in The Jepson Manual. However, according to the Flora of North America, the California hazelnut may be more deserving of subspecific status due to conspicuous differences in habit, leaf shape, pubescence, the presence of glandular hairs, form and size of the involucre, habitat, phytogeography, and several other features.
Known variously as Corylus rostrata var. californica, C. californica, C. cornuta var. glandulosa, and C. rostrata var. tracyi, California hazelnut is the only hazel occurring in California. It forms an open, spreading shrub, six to twenty feet tall, with large, rounded-to-obovate leaves with doubly-serrate margins. Leaves are up to four inches long, velvety-hairy, and with a cordate (heart-shaped) base. Plants are monoecious, meaning both pollen and seeds are produced on the same plant, but the flowers are either male or female, the latter in pendulous catkins. Unlike the birches, the male and female flowers of hazelnuts develop at the same time, generally January through April. The small, edible nuts appear from May through autumn.
California hazelnut occurs in many plant communities, but typically is restricted to moist shady sites, often near streams. It grows in forests along the coast from the Santa Cruz Mountains to Del Norte County, and inland along the western slopes of the Sierra Nevada from Tulare County north into the Klamath and Cascade ranges. The distribution of California hazelnut extends through Oregon and Washington into British Columbia. It occurs from sea level to as high as 7,000 feet. A distribution map can be seen at http://www.efloras.org/object_page.aspx?object_id=6001&flora_id=1 .
Despite its large range, California hazelnut is quite rare on the northern San Francisco Peninsula. In A Flora of San Francisco, California (1958) Howell, Raven, and Rubtzoff cite recorded locations at Laguna Honda, the gully east of Lake Merced, Strawberry Hill in Golden Gate Park, and the Mission Hills. Unfortunately, the only known extant locations in San Francisco County are Yerba Buena Island, Fort Point, and Brotherhood Way. To the south, California hazelnut can be found on San Bruno Mountain, Montara Mountain, and throughout the Santa Cruz Mountains. (Don’t miss Randy Zebell’s Montara Mountain Hazelnut Trail field trip on Sunday, February 26!) To the north, it can be found on Angel Island, the Tiburon Peninsula, and from Mt. Tamalpais to the Point Reyes Peninsula and beyond. In the East Bay, it occurs in the Oakland-Berkeley hills and on Mount Diablo.
Native Americans used California hazelnut twigs in basketry. Stems were scraped with a sharp rock or peeled with teeth, and the stripped stems and inner bark were used for thread, rimhoops, baskets, and sieves. As an excellent source of protein, the nuts were ground into flour and used in bread. In the eastern United States, American hazel was used by native Americans medicinally for hives, biliousness, diarrhea, cramps, hay fever, childbirth, hemorrhages, prenatal strength, and teething, to induce vomiting, and to heal cuts. It is considered a useful horticultural plant and is available at commercial nurseries. Its cultivation and transport, however, should take into consideration that it is an associated host for sudden oak death, which is caused by the fungal pathogen Phytophthora ramorum.
California hazelnut is not listed as rare or endangered under the state or federal endangered species acts, nor is it on any of the rare lists maintained by the California Native Plant Society. In San Francisco, it has been added to the Yerba Buena Chapter’s recently created draft list of locally significant plants.