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