walnut, common name for some members of the Juglandaceae, a family of chiefly deciduous, resinous trees characterized by large and aromatic compound leaves. Species of the walnut family are indigenous mostly to the north temperate zone, but also range from Central America along the Andes to Argentina and through tropical Asia to Java and New Guinea.

Common Species and Their Uses

Several trees of the Juglandaceae are of commercial importance for the edible nuts and for lumber. The "nuts"(they are actually drupelike), usually enclosed in a leathery or woody hull, include many of the most valuable food nuts of the United States—the walnut and the butternut of the walnut genus Juglans and the pecan, hickory nut, pignut, and mockernut of the hickory genus Carya. The single-seeded nuts contain no endosperm; the edible portion is the corrugated, meaty seed leaves of the embryo itself. Lumber is obtained chiefly from Juglans, Carya, and Engelhardia. The latter genus is now restricted to East Asia, but fossil trees have been found in the United States. Species of these and other genera (e.g., Pterocarya, the Asian wingnuts) are often planted as ornamental shade trees.

The walnut genus Juglans (from Lat. Jovis glans=nut of Jove) is the largest and most widely distributed genus of the family. The dark timber of the black walnut (J. nigra), found in hardwood forests in the eastern half of North America, and of the Persian, or English, walnut (J. regia), native to W Asia, is unusually hard and durable and is valued for furniture, interior paneling, gunstocks, musical instruments, and other uses. Black walnut has been the foremost cabinet wood of North America since colonial times.

The closer-grained English walnut, usually sold as lumber under the name Circassian walnut, is widely cultivated in S Europe and the Orient and has been introduced with great success into California, now the major producing area of the world. The nut of this tree is more easily extracted from the shell than that of the black walnut and is the one usually sold commercially for use as a table nut and for confectionery, flavorings, and sometimes pickling. A decoction of the leaves, bark, and hulls has been used for a brown wool dye and the crushed leaves for an insect repellent.

The butternut, or white walnut (J. cinerea), of approximately the same range as the black walnut, has a sweet and oily nut that is gathered locally but is not of commercial importance. The butternut is also timbered; the wood is softer than that of the black and English walnuts. Sugar is sometimes obtained from its sap, and the hulls yield a yellow to gray dye that gave color to the homespun of pioneers and to the "butternut" uniforms of some Confederate soldiers. The inner root bark, called butternut bark, has been used in domestic remedies, as have the hulls of the English walnut. Other American and Old World walnuts are also used and esteemed locally for timber, dyes, and food.

Classification

The walnut family is classified in the division Magnoliophyta, class Magnoliopsida, order Juglandales.

Walnut Creek, residential city (1990 pop. 60,569), Contra Costa co., W Calif., in the San Francisco Bay area; inc. 1914. It is the trade and shipping center of an extensive agricultural area where walnuts, apples, vegetables, and nursery stock are among the major products. There is food processing and the manufacture of machinery, industrial glass, chemicals, medical instruments, and electronic equipment. Business growth developed greatly in the city and its environs in the late 20th cent., and industry has become increasingly important to the economy. Numerous industrial research firms, corporate headquarters, and a naval weapons station are in Walnut Creek.

Walnut Canyon National Monument: see National Parks and Monuments (table).

Any of about 20 species of deciduous trees in the genus Juglans, family Juglandaceae. Black walnut (J. nigra) of eastern North America and English, or Persian, walnut (J. regia), native to Iran, are valuable timber trees that produce edible nuts. The butternut (J. cinerea) of eastern North America also produces an edible nut. The walnut family contains an additional seven genera of flowering plants, found mainly in the northern temperate zone in a variety of habitats. Pecan and hickory are among the many family members that are prized for both their edible nuts and their strong, attractive woods, especially noted for their grain patterns and lustre. Leaves of the walnut family are feather-like; tiny, resinous scales that look like yellow dots on the undersurface of the leaflets give Juglans species a pungent aroma.

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National monument, north-central Arizona, U.S. Established in 1915 and covering an area of 3 sq mi (8 sq km), it preserves more than 300 pre-Columbian dwellings built by the Pueblo Indians in shallow caves on the canyon walls. Main occupancy was from AD 1000 to 1200.

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