Juglans regia, the Persian walnut, English walnut, especially in Great Britain, common walnut, or especially in the US, California walnut, is an Old World walnut tree species native to the region stretching from the Balkans eastward to the Himalayas and southwest China. The largest forests are in Kyrgyzstan, where trees occur in extensive, nearly pure walnut forests at 1,000–2,000 m altitude (Hemery 1998)—notably at Arslanbob in Jalal-Abad Province.

in winter, France

Description[edit]

Juglans regia is a large, deciduous tree attaining heights of 25–35 m, and a trunk up to 2 m diameter, commonly with a short trunk and broad crown, though taller and narrower in dense forest competition. It is a light-demanding species, requiring full sun to grow well.

The bark is smooth, olive-brown when young and silvery-grey on older branches, and features scattered broad fissures with a rougher texture. Like all walnuts, the pith of the twigs contains air spaces; this chambered pith is brownish in color. The leaves are alternately arranged, 25–40 cm long, odd-pinnate with 5–9 leaflets, paired alternately with one terminal leaflet. The largest leaflets are the three at the apex, 10–18 cm long and 6–8 cm broad; the basal pair of leaflets are much smaller, 5–8 cm long, with the margins of the leaflets entire. The male flowers are in drooping catkins 5–10 cm long, and the female flowers are terminal, in clusters of two to five, ripening in the autumn into a fruit with a green, semifleshy husk and a brown, corrugated nut. The whole fruit, including the husk, falls in autumn; the seed is large, with a relatively thin shell, and edible, with a rich flavour.

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  Taxonomic keys

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  Male flower

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  Female flower

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  Fruit

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  Seed

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  Bark

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  Foliage

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  Habit

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  Habit (Autumn)

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  Walnuts

Etymology[edit]

The Latin name for the walnut was nux Gallica, "Gallic nut";^[1] the Gaulish region of Galatia in Anatolia lies in highlands at the western end of the tree's presumed natural distribution.

For the etymology and meaning of the word in English and other Germanic languages, see our article "walnut".

"Walnut" does not distinguish the tree from other species of Juglans. Other names include common Walnut in Britain; Persian walnut in South Africa^[2] and Australia;^[3] and English walnut in North America and Great Britain,^[4] New Zealand,^[5] and Australia,^[3] the latter name possibly because English sailors were prominent in Juglans regia nut distribution at one time.^[6] Alternatively, Walter Fox Allen stated in his 1912 treatise What You Need to Know About Planting, Cultivating and Harvesting this Most Delicious of Nuts:^[7] "In America, it has commonly been known as English walnut to distinguish it from our native species."

In the Chinese language, the edible, cultivated walnut is called 胡桃 (hú táo in Mandarin), which means literally "Hu peach", suggesting the ancient Chinese associated the introduction of the tree into East Asia with the Hu barbarians of the regions north and northwest of China. In Mexico, it is called nogal de Castilla,^[8] suggesting the Mexicans associated the introduction of the tree into Mexico with Spaniards from Castile (as opposed to the black walnuts native of America).

The Old English term wealhhnutu is a late book-name (Old English Vocabularies, Wright & Wulker), so the remark that the Anglo-Saxons inherited the walnut tree from the Romans does not follow from this name.

Distribution and habitat[edit]

Original habitat[edit]

Juglans regia is native to the mountain ranges of Central Asia, extending from Xinjiang province of western China, parts of Kazakhstan, Uzbekistan and southern Kirghizia and from lower ranges of mountains in Nepal, Bhutan, Tibet, northern India and Pakistan, through Afghanistan, Turkmenistan and Iran to portions of Azerbaijan, Armenia, Georgia and eastern Turkey. In these countries, there is a great genetic diversity, in particular ancestral forms with lateral fruiting. During its migration to western Europe, the common walnut lost this character and became large trees with terminal fruiting. A small remnant population of these J. regia trees have survived the last glacial period in Southern Europe^{[citation needed]}, but the bulk of the wild germplasm found in the Balkan peninsula and much of Turkey was most likely introduced from eastern Turkey by commerce and settlement several thousand years ago^{[citation needed]}.

Introduction around the world[edit]

In the fourth century BC, Alexander the Great introduced this "Persian nut" (Theophrastus' καρυα ή Περσική^[9]) in Macedonian and Greek ancestral forms with lateral fruiting from Iran and Central Asia. They hybridized with terminal-bearing forms to give lateral-bearing trees with larger fruit^{[clarification needed]}. These lateral-bearers were spread in southern Europe and northern Africa by Romans. Recent prospections in walnut populations of the Mediterrean Basin allowed to select interesting trees of this type. In the Middle Ages, the lateral-bearing character was introduced again in southern Turkey by merchants travelling along the Silk Road. J. regia germplasm in China is thought to have been introduced from Central Asia about 2000 years ago, and in some areas has become naturalized. Cultivated J. regia was introduced into western and northern Europe very early, in Roman times or earlier, and to the Americas in the 17th century, by English colonists. Important nut-growing regions include France, Serbia, Greece, Bulgaria, Romania and Hungary in Europe, China in Asia, California in North America, and Chile in South America. Lately, cultivation has spread to other regions, such as New Zealand and the southeast of Australia.^[10] It is cultivated extensively from 30° to 50° of latitude in the Northern Hemisphere and from 30° to 40° in the Southern Hemisphere. Its high-quality fruits are eaten both fresh or pressed for their richly flavored oil; numerous cultivars have been selected for larger nuts with thinner shells.

It is also cultivated as a handsome ornamental specimen tree in parks and large gardens. As such, it has gained the Royal Horticultural Society's Award of Garden Merit.^[11]

Cultivars[edit]

See list of most planted cultivars in article Walnut

J. regia 'Buccaneer' produces an abundant crop of seeds. A self-fertile cultivar, it produces pollen over a long period and is thus a valuable pollinator for other cultivars. The tree is about the same size as an open-pollinated walnut, it comes into leaf very late and so usually avoids damage by late frosts.

Life cycle[edit]

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  Buds

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  Young tree

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  Fertilized flowers

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  Mature tree

Nutritional value[edit]

A study of ten cultivars of J. regia in Turkey showed significant variations in fatty acid content of the nuts:^[12]

• 62% - 71% fat
  • saturated fat (as a percentage of total fatty acids):
    • 5.2% - 7.3% palmitate
    • 2.6% - 3.7% stearate
  • unsaturated fat (as a percentage of total fatty acids):
    • 21.2% - 40.2% oleate (monounsaturated)
    • 43.9% - 60.1% linoleate (diunsaturated)
    • 6.9% - 11.5% linolenate (triunsaturated)

Potential biological effects[edit]

Walnuts and other tree nuts are important food-allergen sources that have the potential to be associated with life-threatening, IgE-mediated systemic reactions in some individuals.^[13][14]

Certain extracts of walnuts have in vitro antioxidant and antiproliferative activity due to a high phenolic content.^[15]

In vitro tests of walnut extract have shown a high antiatherogenic potential and osteoblastic activity, suggesting a potential beneficial effect of a walnut-enriched diet on cardioprotection and bone loss.^[16]

The extract from walnut leaves is an antioxidant, decreases the blood sugar level and has a positive impact on lipid metabolism. The extract suppresses functional insufficiency of liver, links synthethising enzymes, increases the antitoxic action of hepatocytes and improves the functional insufficiency of kidneys.^[17] The ethanolic extract from leaves of J. regia has an antidiabetic effect on diabetes-induced rats.^[18]

Bark and leaf crude extracts of J. regia, and J. mollis, showed in vitro activity against Mycobacterium tuberculosis.^[19]

Culture[edit]

In Skopelos, a Greek island in the Aegean Sea, local legend suggests whoever plants a walnut tree will die as soon as the tree can "see" the sea^{[citation needed]}. Most planting is done by field rats (subfamily Murinae). In Flanders, a folk saying states: "By the time the tree is big, the planter surely will be dead." (Dutch: Boompje groot, plantertje dood). This saying refers to the relatively slow growth rate of the tree.

In rural villages of the Rađevian region of western Serbia, the head of household would crack a walnut on Christmas morning. If the walnut was sound, it was thought that the coming year would be prosperous. If the walnut was shrivelled, the head of household would avert the bad omen by running three times around his house, at the same time shouting what could be paraphrased as "Do not listen, God, to Jack, who is full of cack."^[20]

Cultivation[edit]

Walnut trees grow best in rich, deep soil with full sun and long summers, such as the California central valley. In the U.S., J. regia is often grafted onto a rootstock of a native black walnut, Juglans hindsii to provide disease resistance. Other plants often will not grow under walnut trees because the fallen leaves and husks contain juglone, a chemical which acts as a natural herbicide. Horses that eat walnut leaves may develop laminitis, a hoof ailment. Mature trees may reach 50 feet in height and width, and live more than 200 years, developing massive trunks more than eight feet thick.

Other uses[edit]

Walnut heartwood is a heavy, hard, open-grained hardwood. Freshly cut live wood may be Dijon-mustard colour, darkening to brown over a few days. The dried lumber is a rich chocolate-brown to black, with cream to tan sapwood, and may feature unusual figures, such as "curly", "bee's wing", "bird's eye", and "rat tail", among others. It is prized by fine woodworkers for its durability, lustre and chatoyance, and is used for high-end flooring, guitars, furniture, veneers, knobs and handles as well as Gunstocks.

Methyl palmitate, which has been extracted from green husks of J. regia has insecticidal properties: at a concentration of 10 mg/ml, it killed 98% of Tetranychus cinnabarinus (carmine spider mites) in one study.^[21]

See also[edit]

Food portal

• Black walnut
• Taxonomy of walnut tree varieties

Notes[edit]

References[edit]

• Flora Europaea: Juglans regia
• Flora of Pakistan: Juglans regia
• Chauhan, N., Wang, K.C., Wegiel, J. and Malik, M.N. (2004) "Walnut Extract Inhibits the Fibrillization of Amyloid Beta-Protein, and also Defibrillizes its Preformed Fibrils", Current Alzheimer Research, 1 (3), p. 183–188
• Hemery, G. E. (1998). Walnut seed-collecting expedition to Kyrgyzstan in Central Asia. Quarterly Journal of Forestry 92 (2): 153-157.
• Society for Neuroscience (2007). "News Release: Diet of walnuts, blueberries improve cognition; may help maintain brain function", Society for Neuroscience, 5 November 2007
• eFloras, Missouri Botanical Garden & Harvard University Herbaria (FOC Vol. 4 Page 282). "Juglans regia". Retrieved 2009. 

A walnut is an edible seed of any tree of the genus Juglans, especially the Persian or English walnut, Juglans regia. Broken nutmeats of the eastern black walnut from the tree Juglans nigra are also commercially available in small quantities, as are foods prepared with butternut nutmeats from Juglans cinerea.

Walnut seeds are a high density source of nutrients, particularly proteins and essential fatty acids. Walnuts, like other tree nuts, must be processed and stored properly. Poor storage makes walnuts susceptible to insect and fungal mold infestations; the latter produces aflatoxin - a potent carcinogen. A mold infested walnut seed batch should not be screened and then consumed; the entire batch should be discarded.^[1]

Walnut seed shell inside its green husk

Walnuts are rounded, single-seeded stone fruits of the walnut tree. The walnut fruit is enclosed in a green, leathery, fleshy husk. This husk is inedible. After harvest, the removal of the husk reveals the wrinkly walnut shell, which is in two halves. This shell is hard and encloses the kernel, which is also made up of two halves separated by a partition. The seed kernels - commonly available as shelled walnuts - are enclosed in a brown seed coat which contains antioxidants. The antioxidants protect the oil-rich seed from atmospheric oxygen so preventing rancidity.^[1]

The two most common major species of walnuts are grown for their seeds — the Persian or English Walnut and the Black Walnut. The English Walnut (J. regia) originated in Persia, and the Black Walnut (J. nigra) is native to eastern North America. The Black walnut is of high flavor, but due to its hard shell and poor hulling characteristics it is not grown commercially for nut production. The commercially produced walnut varieties are nearly all hybrids of the English walnut.^[2]

Other species include J. californica, the California Black Walnut (often used as a root stock for commercial breeding of J. regia), J. cinerea (butternuts), and J. major, the Arizona Walnut.

Walnuts are late to bear leaves, typically not until more than halfway through the spring. They also secrete chemicals into the soil to prevent competing vegetation from growing. Because of this, flowers or vegetable gardens should not be planted too close to them.

The husks of walnut contains a juice that will readily stain anything it comes into contact with. It has been used as a dye for cloth.

Production

The worldwide production of walnut seeds has been increasing rapidly in recent years, with most increase coming from Asia. The world produced a total of 2.55 million metric tonnes of walnut seeds in 2010; China was the world's largest producer of walnut seeds, with a total harvest of 1.06 million metric tonnes.^[3] The other major producers of walnut seeds were (in the order of decreasing harvest): United States, Iran, Turkey, Ukraine, Mexico, Romania, India, France and Chile.

The average worldwide walnut seed yield was about 3 metric tonnes per hectare, in 2010. Among the major producers, eastern European countries have the highest yield. According to the FAO, the most productive walnut seed farms in 2010 were in Romania, with yields above 23 metric tonnes per hectare.^[4]

The United States is the world's largest exporter of walnut seeds. The Sacramento and San Joaquin valleys of California produce 99 percent of the nation’s commercial English walnut seeds.

Storage

The ideal temperature for longest possible storage of walnut seeds is in the -3 to 0 ^oC and low humidity - for industrial and home storage. However, such refrigeration technologies are unavailable in developing countries where walnuts are produced in large quantities; there, walnut seeds are best stored below 25 ^oC and low humidity. Temperatures above 30 ^oC, and humidities above 70 percent can lead to rapid and high spoilage losses. Above 75 percent humidity threshold, fungal molds that release dangerous aflatoxin can form.^[1][5]

Freshly harvested raw walnut seeds with water content between 2 to 8 percent offer the best color, flavor and nutrient density.

Nutritional value

Walnut, English

Persian or English walnut, Juglans regia
Nutritional value per serving
Serving size	100 grams
Energy	2,738 kJ (654 kcal)
Carbohydrates	13.71
- Starch	0.06
- Sugars	2.61
- Lactose	0
- Dietary fiber	6.7
Fat	65.21
- saturated	6.126
- monounsaturated	8.933
- polyunsaturated	47.174
Protein	15.23
Water	4.07
Alcohol	0
Caffeine	0
Vitamin A equiv.	1 μg (0%)
Vitamin A	20 IU
- beta-carotene	12 μg (0%)
- lutein and zeaxanthin	9 μg
Thiamine (vit. B1)	0.341 mg (30%)
Riboflavin (vit. B2)	0.15 mg (13%)
Niacin (vit. B3)	1.125 mg (8%)
Pantothenic acid (B5)	0.570 mg (11%)
Vitamin B6	0.537 mg (41%)
Folate (vit. B9)	98 μg (25%)
Vitamin B12	0 μg (0%)
Vitamin C	1.3 mg (2%)
Vitamin D	0 μg (0%)
Vitamin D	0 IU (0%)
Vitamin E	0.7 mg (5%)
Vitamin K	2.7 μg (3%)
Calcium	98 mg (10%)
Iron	2.91 mg (22%)
Magnesium	158 mg (45%)
Manganese	3.414 mg (163%)
Phosphorus	346 mg (49%)
Potassium	441 mg (9%)
Sodium	2 mg (0%)
Zinc	3.09 mg (33%)
Percentages are relative to US recommendations for adults. Source: USDA Nutrient Database

Walnuts are one of the several high nutrient density foods. 100 grams of walnuts contain 15.2 gram protein, 65.2 gram fat, and 6.7 gram dietary fiber. The protein in walnuts provides many essential amino acids.

While English walnut is the predominant commercially distributed nut because of the ease of its processing, its nutrient density and profile is significantly different from black walnut. The table below compares some of the major nutrients between English and Black walnuts.

Unlike most nuts that are high in monounsaturated fatty acids, walnuts are composed largely of polyunsaturated fatty acids (47.2 grams), particularly alpha-linolenic acid (18:3n - 3; 9.1 gram) and linoleic acid (18:2n - 6; 38.1 gram). The beneficial effects of this unique fatty acid profile has been a subject of many studies and discussions. Banel and Hu concluded in 2009 that while walnut-enhanced diets are promising in short term studies, longer term studies are needed to ascertain better insights.^[7]

Medical benefits and claims

A whole walnut kernel, with both halves unbroken.

Raw walnuts contain glyceryl triacylates of the n-3 fatty acid alpha-linolenic acid (ALA),^[8] which is not as effective in humans as long-chain n-3 fatty acids,^[9] and (mostly insoluble) antioxidants.^{[10][11][12][13][14]} Roasting reduces antioxidant quality.^[15] In 2010, a report^{[citation needed]} published in the Journal of the American College of Nutrition said that walnuts and walnut oil improve reaction to stress.^[16]

A study has suggested that consumption of walnuts increases fat oxidation and reduces carbohydrate oxidation without affecting total consumption, suggesting that walnut consumption may improve the use of body fat in overweight adults.^[17] Walnuts have been shown to decrease the endothelial dysfunction associated with a high-fat meal.^[18] Aged rats fed diets containing 2% to 6% walnuts showed reversal of age-associated motor and cognitive function, but a 9% walnut diet impaired performance, suggesting a J curve.^[19]

On October 11, 2006, ScienceDaily published a report^[20] which stated "New research shows that consuming a handful of raw walnuts along with meals high in saturated fat appears to limit the ability of the harmful fat to damage arteries," and attributed the result to a 2006 article in the Journal of the American College of Cardiology. The lead researcher, Emilio Ros, MD, PhD, was quoted as saying "People would get the wrong message if they think that they can continue eating unhealthy fats provided they add walnuts to their meals."^[20] Funding for the study was provided by the California Walnut Commission, an industry marketing agency.^[20]

A 2012 study showed that eating walnuts improved sperm quality in healthy young men.^[21][22]

Medicinal uses

Scientists are not yet certain whether walnuts act as a cancer chemopreventive agent, an effect which may be a result of the fruit's high phenolic content, antioxidant activity, and potent in vitro antiproliferative activity.^[23]

Compared to certain other nuts, such as almonds, peanuts and hazelnuts, walnuts (especially in their raw form) contain the highest total level of antioxidants, including both free antioxidants and antioxidants bound to fiber.^[11]

Chemical analysis

To remove the husk from kernel can lead to hand staining. Walnut hulls contain phenolics that stain hands and can cause skin irritation. Seven phenolic compounds (ferulic acid, vanillic acid, coumaric acid, syringic acid, myricetin, juglone^[24] and regiolone^[25]) have been identified in walnut husks by using reverse phase-high performance liquid chromatography or crystallography.

Walnuts also contain the ellagitannin pedunculagin.^[26]

(−)-Regiolone has been isolated with juglone, betulinic acid and sitosterol from the stem-bark of J. regia.^[27]

Investment in China

In China, pairs of walnuts have traditionally been rotated and played with in the palm of the hand, both as a means to stimulate blood circulation and as a status symbol. Pairs of large, old and symmetrically shaped walnuts are valued highly and have recently been used as an investment, with some of them fetching tens of thousands of dollars.^[28] Pairs of walnuts are also sometimes sold still in their green skin, as a form of gambling known as du he tao.^[29]

Etymology and names

Etymologically, the word walnut derives from the Germanic wal- and Old English wealhhnutu, literally "foreign nut", wealh meaning "foreign" (wealh is akin to the terms Welsh and Vlach; see Walha).^[30]

In certain parts of the world, walnuts are locally known as Gerdoo,walnüsse, noix, nuéz, noz, nuc, ceviz, orah (орах), enkuyz (ընկոյզ), akharōṭ (अखरोट), kurumi (胡桃), hétáo (核桃), hodu (호두).

Cultivars

• 'Chandler'
• 'Hartley"
• 'Lara'
• 'Franquette'
• 'Mayette'
• 'Marbot'
• 'Mellanaise'
• 'Parisienne'
• 'Germisara'
• 'Jupanesti'
• 'Serr'
• 'Vina'
• 'Valcor'

See also

• Nut (fruit)