J. duclouxianaDode J. fallaxDode J. kamaonica(C. de Candolle)Dode J. orientisDode J. regia subsp.fallax(Dode)Popov J. regia subsp.kamaonica(C. de Candolle)Mansf. J. regia subsp.turcomanicaPopov J. regia var.orientis(Dode)Kitam. J. regia var.sinensisC. de Candolle J. sinensis(C. de Candolle)Dode
Juglans regia, thecommon walnut[1] orPersian walnut[2] amongst other regional names, is a species ofwalnut. It is native to Eurasia in at least southwest and central Asia and southeast Europe, but its exact natural area is obscure due to its long history of cultivation.
The species has numerouscultivars which produce the ediblewalnut consumed around the world and produced predominately in China. It is widely cultivated across temperate regions throughout the world including those of Eurasia, Australia, and the Americas.
Juglans regia is a largedeciduous tree, attaining heights of 10–25 metres (35–80 feet), and a trunk up to 2 m (6+1⁄2 ft) in diameter, commonly with a short trunk and broad crown.[3][4] The tallest accurately measured specimen is inLagodekhi Protected Areas inGeorgia, 29 m (95 ft) tall, and the stoutest, 9 m (30 ft) girth (2.87 m (9 ft 5 in) diameter);[5] heights of 34 m in the wild in Kyrgyzstan,[6] and 32 m in cultivation in Britain[7] have been reported, but not verified.
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, thepith of the twigs contains air spaces; this chambered pith is creamy-white at first, becoming brown in older twigs. Theleaves are alternately arranged,20–45 cm (8–17+1⁄2 in) long, odd-pinnate with (3–)5–9 (most often 7) leaflets, arranged in opposite pairs with one terminal leaflet. The largest leaflets are the three at the apex, 10–20 cm (4–8 in) long and6–10 cm (2+1⁄2–4 in) broad; the basal pair of leaflets are much smaller, 5–8 cm (2–3 in) long. The margins of the leaflets are entire, but with toothed margins on seedlings, and in thecultivar 'Laciniata'. The leaves open fairly late in the spring (typically mid May in Britain), and are red-brown at first, becoming their mature dark yellow-toned green by mid June. The male flowers are in droopingcatkins 5–10 cm (2–4 in) long, and the female flowers are terminal, in clusters of two to five, ripening in the autumn into afruit with a green, semi-fleshy husk and a brown, corrugatednut. The whole fruit, including the husk, falls in autumn with the husk breaking open; theseed is a large and ediblenut with a rich flavour; the shell is thick in wild populations, while most cultivated plants have been selected for a thin shell.[3][4]
Seedling; note the serrated leaf margins
Young tree
Mature tree
Bark
Buds
The new leaves in spring have a distinctive red-brown colour at first
One of the centres of origin and diversity ofJ. regia is Iran,[8][9] and another further northeast in Central Asia.[2] In Central Asia, genetic diversity is very patchy, with the highest diversity found aroundSariosiyo inUzbekistan,[2] and conspicuously lower in the famousArslanbob forests[2] (these now thought to be of cultivated origin).[10] Another native glacial refugium population with high genetic diversity is found on the southern fringes of the Alps in northeast Italy.[11] However, as with other old and widespread cultivated plants, it is not easy to reconstruct the original distribution and determine the borders of the past natural ranges. There are many reports concerning the earliest fossil pollen and nuts ofJ. regia, and the conclusions that various authors draw are somewhat contradictory. Taken together these finds suggest thatJ. regia possibly survived the last glaciations in several refugia, as the compilation of the data shows most likely southern Europe, the Near East, China, and the Himalaya.[10]
The largest forests are in Kyrgyzstan, where trees occur in extensive forests at 1,000–2,000 metres (3,300–6,600 ft) altitude,[6] notably atArslanbob inJalal-Abad Province.[12]
In the fourth century BC,Alexander the Great introduced this "Persian nut" (Theophrastus' καρυα ή Περσική)[13] in Macedonian, Ancient 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 Mediterranean 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 2,000 years ago, and in some areas has becomenaturalised. CultivatedJ. regia was introduced into western and northern Europe very early, probably inRoman times,[3] and to the Americas in the 17th century, by European colonists. Important nut-growing regions include California in the United States; France,Serbia, Greece,Bulgaria,Romania and Hungary in Europe; China in Asia;Baja California andCoahuila inMexico; andChile in Latin America. Lately, cultivation has spread to other regions, such as New Zealand and the southeast of Australia.[14] 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 flavoured oil; numerouscultivars have been selected for larger nuts with thinner shells.[15]
J. regia is highly diversegenetically, and has been extensively cultivated for possibly as long as 2,000 years in parts ofwest Asia and southern Europe.[2][11]
Its closest relative isJuglans sigillata from western China and the far northeast of India;[16] it differs chiefly in leaves with 9–11 leaflets, and nuts with a much thicker, harder shell.[17]
It tends to grow taller and narrower in dense forest competition. It is a light-demanding species, requiring full sun to grow well.[4]
Juglans regia is infested byRhagoletis juglandis, commonly known as the walnut husk fly, which lays its eggs in the husks of walnut fruit.[18]
Other plants often will not grow under walnut trees because the fallen leaves and husks containjuglone, a chemical which acts as a naturalherbicide. Horses that eat walnut leaves may developlaminitis, a hoof ailment.[citation needed]
Walnut trees grow best in rich, deep soil with full sun and long summers, such as the California central valley.Juglans hindsii andJ. hindsii ×J. regia are often used as grafting stock forJ. regia.[20] Mature trees may reach 15 m (50 ft) in height and width, and live more than 200 years, developing massive trunks more than 2.4 m (8 ft) thick.
FLORY 34 Series Nut Sweeper during harvest inGlenn County, California
FLORY 8770 Harvester during walnut harvest in Glenn County
Particular cultivars ofJ. regia may be more infested byR. juglandis than others because of varying walnut husk softness or thickness. 'Eureka', 'Klondike', 'Payne', 'Franquette' and 'Ehrhardt' cultivars are among the most susceptible to infestation.[21]
In 2022, world production of shelled walnuts was 3.9 milliontonnes, led by China with 36% of the total harvested, with the United States, Iran, and Turkey as secondary producers (table).
As with all species of walnut, the green outer husk of the fruit is rich in a yellow-brown to dark browndye; harvesting the nuts often leaves the fingers strongly stained brown, and an extract from the husks can be used for dyeing cloth. The dye has notable antibacterial properties.[26]
Walnutheartwood 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 tansapwood, 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 andchatoyance, and is used for high-endflooring,guitars,furniture,veneers,knobs and handles as well asgunstocks.[27]
InSkopelos, 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.[28] Most planting is done by field rats (subfamilyMurinae). InFlanders, a folksaying states: "By the time the tree is big, the planter surely will be dead." (Dutch:Boompje groot, plantertje dood). These sayings refer to the relatively slow growth rate and late fruiting of the tree.[29]
Benevento in southern Italy is the home of an ancient tradition ofstregoneria. Thewitches of Benevento were reputed to come from all over Italy to gather for theWitches' Sabbath under the sacred walnut tree of Benevento. In 1526, JudgePaolo Grillandi wrote of witches in Benevento who worship a goddess at the site of an old walnut tree.[30] This legend inspired many cultural works, including the 1812 balletIl Noce di Benevento (the walnut tree of Benevento) bySalvatore Viganò andFranz Xaver Süssmayr, a theme from which was adapted into a violin piece calledLe Streghe byNiccolò Paganini.[31] The Beneventan liqueurStrega depicts on its label the famous walnut tree with the witches dancing under it.[32]
TheLatin name for the walnut wasnux Gallica, "Gallic nut";[33] the Gaulish region ofGalatia inAnatolia lies in highlands at the western end of the tree's presumed natural distribution.
Although often called simply "walnut",[4] this does not distinguish the tree from other species ofJuglans. Internationally, it is most often called "common walnut"[1][2][6] or "Persian walnut";[11][2][34][35][36] other names include "Madeira walnut",[37] and "English walnut" mainly in North America,[38] possibly because English sailors were prominent inJuglans regia nut distribution at one time.[39]Alan Mitchell comments "The Americans call it 'English Walnut', which is plainly an error by the early settlers when finding the Black Walnut and Butternut growing in their woods, and 'Persian Walnut', which is correct",[7] and Walter Fox Allen stated in his 1912 treatiseWhat You Need to Know About Planting, Cultivating and Harvesting this Most Delicious of Nuts:[40] "In America, it has commonly been known as English walnut to distinguish it from our native species", and occasionally elsewhere.[36][41] The name "Carpathian walnut" refers to acultivar group of selected cold-tolerant strains with high quality nuts, rather than the species as a whole.[15]
In theChinese language, the edible, cultivated walnut is called胡桃 (hú táo in modern standard Chinese), which means literally "Hu peach", suggesting the ancient Chinese associated the introduction of the tree into East Asia with theHu barbarians of the regions north and northwest of China.[citation needed] In Mexico, it is callednogal de Castilla,[42] suggesting the Mexicans associated the introduction of the tree into Mexico with Spaniards fromCastile (as opposed to theblack walnuts native to North America).[citation needed]
The Old English termwealhhnutuis a late book-name[clarification needed] (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. Old English: walhhnutu is wealh (foreign) + hnutu (nut). Etymologically it "meant the nut of the Roman lands (Gaul and Italy) as distinguished from the nativehazel" according to the Oxford English Dictionary.[citation needed]
^abHuxley A (1992).Dictionary of Gardening (Royal Horticultural Society, UK). London; New York: Macmillan Press; Stockton Press.ISBN1-56159-001-0.
^Aradhya MK, Potter D, Simon CJ (31 December 2006). "7. Cladistic Biogeography of Juglans ( Juglandaceae) Based on Chloroplast DNA Intergenic Spacer Sequences".Darwin's Harvest(PDF). Columbia University Press. pp. 143–170.doi:10.7312/motl13316-008.ISBN978-0-231-16891-5.
^"Walnuts in California". Fruit and Nut Research and Information Center, University of California at Davis. 2021. Archived fromthe original on 17 November 2020. Retrieved23 January 2021.
^Boyce, A.M. (December 1929). "The Walnut Husk Fly (Rhagoletis juglandis Cresson)".Journal of Economic Entomology.22: 861–866.
.jpg)
