Juglans regia

Juglans regia is a large deciduous tree, attaining heights of 25–35 metres (80–120 feet), and a trunk up to 2 m (6 ft) in diameter, commonly with a short trunk and broad crown.

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 (10 to 16 in) 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 (4 to 7 in) long and 6–8 cm (2 to 3 in) broad; the basal pair of leaflets are much smaller, 5–8 cm (2 to 3 in) long, with the margins of the leaflets entire. The male flowers are in drooping catkins 5–10 cm (2 to 4 in) 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.

Taxonomic keys

The Latin name for the walnut was nux Gallica, "Gallic nut";[3] 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 "walnut".

"Walnut" does not distinguish the tree from other species of Juglans. Other names include common walnut in Britain; Persian walnut in South Africa[4] and Australia;[5] and English walnut in North America and Great Britain,[6] New Zealand,[7] and Australia,[5] the latter name possibly because English sailors were prominent in Juglans regia nut distribution at one time.[8] Alternatively, Walter Fox Allen stated in his 1912 treatise What You Need to Know About Planting, Cultivating and Harvesting this Most Delicious of Nuts:[9] "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,[10] suggesting the Mexicans associated the introduction of the tree into Mexico with Spaniards from Castile (as opposed to the black walnuts native to North 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. Old English: walhhnutu is wealh (foreign) + hnutu (nut). Etymologically it "meant the nut of the Roman lands (Gaul and Italy) as distinguished from the native hazel" according to the Oxford English Dictionary.

It tends to grow taller and narrower in dense forest competition. It is a light-demanding species, requiring full sun to grow well.

Juglans regia is infested by Rhagoletis juglandis, commonly known as the walnut husk fly, which lays its eggs in the husks of walnut fruit.

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.

FLORY 34 Series Nut Sweeper in a walnut orchard during harvest season in Glenn County, California

FLORY 8770 Harvester during walnut harvest in Glenn County, California

Walnut production (shelled) – 2019
Country	(millions of tonnes)
China	2.52
United States	0.59
Iran	0.32
Turkey	0.23
Mexico	0.17
World	4.50
Source: FAOSTAT of the United Nations[16]

Walnut trees grow best in rich, deep soil with full sun and long summers, such as the California central valley. Juglans hindsii and J. hindsii × J. regia are often used as grafting stock for J. regia.[17] 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.

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.[24] 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). These sayings refer to the relatively slow growth rate and late fruiting of the tree.[25]

Benevento in southern Italy is the home of an ancient tradition of stregoneria. The witches of Benevento were reputed to come from all over Italy to gather for their sabbats under the sacred walnut tree of Benevento. In 1526, Judge Paolo Grillandi wrote of witches in Benevento who worship a goddess at the site of an old walnut tree.[26] This legend inspired many cultural works, including the 1812 ballet Il Noce di Benevento (the walnut tree of Benevento) by Salvatore Viganò and Franz Xaver Süssmayr, a theme from which was adapted into a violin piece called Le Streghe by Niccolò Paganini.[27] The Beneventan liqueur Strega depicts on its label the famous walnut tree with the witches dancing under it.[28]

• Taxonomy of walnut tree varieties

• Juglans regia - information, genetic conservation units and related resources. European Forest Genetic Resources Programme
• Flora of Pakistan: Juglans regia