Family: Juglandaceae, contains 2 important genera:
Hickory/Pecan (Carya) and Walnut (Juglans)
See also: Walnut, for information on the nut.
Synonyms: Carya, Jupiter's Nuts, Carya persica (Greek), Carya basilike (Greek).
Californian walnut - Juglans californica
English walnut - Juglans regia.
Black walnut - Juglans nigra.
White walnut or Butternut - Juglans cinerea
Walnut is the common name given to twenty species of deciduous trees in the genus Juglans, of which six species are native to the United States. Walnut is native to California, but about 15 related species occur in North and South America as well as in central and southern parts of Europe and Asia. The largest walnut plantations are in California. J. californica is planted as a shade tree and is often used for rootstock for other walnuts. Its edible nuts are a delicacy, and oils are used by painters and in soap making. The hard wood is important in cabinet making.
The Black walnut is native to the eastern United States, native to Virginia, growing from Maine west to southern Michigan and south to Texas and Georgia. It is important for its timber, used in fine furniture, rather than for its nut, the flesh of which is tasty but surrounded by a hard, thick shell (outer husk) that makes the nut difficult to utilize.
The common or English walnut, which is native to areas stretching from the Balkans to China, extending from Greece and Asia Minor, over Lebanon and Persia, all along to the Himalayas, but now widely grown in many other temperate areas, is one of the most important nut crops grown.
The tree grows to a height of 40 or 60 feet, with a large spreading, rounded top, and thick, massive stem. It occurs in woods and on mountain slopes. Some Walnut trees are 300 years old. Black walnut is the tallest of the walnuts, with the potential to reach 100 feet. The Walnut tree has compound leaves which are spaced alternately along the branches, which consists of small yellowish green leaflets. Walnuts are monoecious, with male flowers borne in long, unbranched, drooping catkins and female flowers borne singly or in short spikes. The walnut fruit is a nut, borne singly or in pairs, and enclosed in a solid, non-splitting green husk. The edible, oil-rich nut kernal is enclosed in a thick, hard, ridged, black shell. Black walnut heartwood is heavy, hard, strong, and durable, with a chocolate-brown color prized by furniture manufacturers and many other industries. The Black walnut is much oilier and richer tasting than that of the English walnut found in grocery stores.
The flowers of separate sexes are borne upon the same tree and appear in early spring before the leaves. The Walnut tree flowers and produces pollen, after 20 to 30 years of growth, in late spring to early summer, extending from April to May in the Northern Hemisphere. The pollen of all these trees is large and does not travel far. However, in areas where the trees are cultivated commercially, heavy exposure to the pollen can cause allergy symptoms. Walnut pollen is generally considered to be moderately allergenic. The western species of walnut (in California) is thought to be a more important cause of allergic sensitization than the Black walnut. The walnut pollens are often the cause of inhalant allergies, and the nuts may cause food allergy.
Some plants planted near or under the Black walnut tree tend to yellow, wilt, and die. This occurs because the walnut tree produces a non-toxic, colorless, chemical called hydrojuglone. Hydrojuglone is found in leaves, stems, fruit hulls, inner bark and roots. When exposed to air or soil compounds, hydrojuglone is oxidized into the juglone, which is highly toxic. The secretion of biochemical materials into the environment to inhibit germination or growth of surrounding vegetation is called allelopathy, which enhances the plants survival and reproduction. Several related trees such as English walnut, hickories and pecan also produce juglone, but in smaller amounts compared to black walnut.
The Walnut tree nut contains a lipid transfer protein allergen (LTP). (Asero 2001 ref.4245 9) (Asero 2000 ref.3711 9) Whether a similar LTP allergen is present in Walnut tree pollen has not been determined yet. Cross-reactivity due to LTP allergens appears to be relevant only in foods, which are ingested, and not in pollens, which are inhaled.
IGE AND IMMUNE:
Pollen from the Walnut tree is commonly found in airborne pollen surveys and will contribute to asthma, hayfever, conjunctivitis, and anaphylaxis. (Sicherer 2000 ref.4559 4) (Shafiee 1976 ref.45720) (Lewis 1975 ref.3257 8)
There is a high cross-reactivity suggested between members of the genus Juglans. (Yman 1982 ref.1241 0)
Occupational allergic contact dermatitis has been observed. (Estlander 2001 ref.4409 7)
Unknown or Nil
Information supplied from an abridged section of:
Allergy Advisor - Zing Solutions
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