Juglans major
Morton Arboretum acc. 614-47*1
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Fagales
Family: Juglandaceae
Subfamily: Juglandoideae
Tribe: Juglandeae
Subtribe: Juglandinae
Genus: Juglans
Type species
Juglans regia

See text

Native ranges of Juglans spp.

Wallia Alef

Walnut trees are any species of tree in the plant genus Juglans, the type genus of the family Juglandaceae, the seeds of which are referred to as walnuts. All species are deciduous trees, 10–40 metres (33–131 ft) tall, with pinnate leaves 200–900 millimetres (7.9–35.4 in), with 5–25 leaflets; the shoots have chambered pith, a character shared with the wingnuts (Pterocarya), but not the hickories (Carya) in the same family.

The 21 species in the genus range across the north temperate Old World from southeast Europe east to Japan, and more widely in the New World from southeast Canada west to California and south to Argentina.

Edible walnuts, which are consumed worldwide, are usually harvested from cultivated varieties of the species Juglans regia. China produces half of the world total of walnuts.


The common name walnut derives from Old English wealhhnutu, literally 'foreign nut' (from wealh 'foreign' + hnutu 'nut'),[2] because it was introduced from Gaul and Italy.[3] The Latin name for the walnut was nux Gallica, "Gallic nut".


Tradition has it that a walnut tree should be beaten. This would have the benefit of removing dead wood and stimulating shoot formation.[4]


Walnut (in shell) production – 2017
Country (tonnes)
 China 1,925,403
 United States 571,526
 Iran 349,192
 Turkey 210,000
 Mexico 147,198
 Ukraine 108,660
World 3,829,626
Source: FAOSTAT of the United Nations[5]

In 2017, world production of walnuts (in shell) was 3.8 million tonnes, led by China with producing half of the world total (table). Other major producers were the United States (15%) and Iran (9%).

Cultivation and uses

Walnut is one of the main ingredients of Baklava and Turkish cuisine.

The two most commercially important species are J. regia for timber and nuts, and J. nigra for timber. Both species have similar cultivation requirements and are widely grown in temperate zones.

Walnuts are light-demanding species that benefit from protection from wind. Walnuts are also very hardy against drought.

Interplanting walnut plantations with a nitrogen fixing plant, such as Elaeagnus × ebbingei or Elaeagnus umbellata, and various Alnus species, results in a 30% increase in tree height and girth (Hemery 2001).

When grown for nuts, care must be taken to select cultivars that are compatible for pollination purposes; although some cultivars are marketed as "self fertile", they will generally fruit better with a different pollination partner. Many different cultivars are available for growers, and offer different growth habits, flowering and leafing, kernel flavours and shell thicknesses. A key trait for more northerly latitudes of North America and Europe is phenology, with ‘late flushing’ being particularly important to avoid frost damage in spring. Some cultivars have been developed for novel ‘hedge’ production systems developed in Europe and would not suit more traditional orchard systems.


The leaves and blossoms of the walnut tree normally appear in spring. The male cylindrical catkins are developed from leafless shoots from the past year; they are about 10 cm (3.9 in) in length and have a large number of little flowers. Female flowers appear in a cluster at the peak of the current year’s leafy shoots.[6]


The fruits of the walnut are a type of accessory fruit known as a pseudodrupe (or drupe-like nut), the outer covering of the fruit is an involucre - in a drupe the covering would be derived from the carpel.[7]

Nuts and kernels

Persian walnut (Juglans regia) seeds

The nut kernels of all the species are edible, but the walnuts most commonly traded are from the J. regia, the only species which has a large nut and thin shell. J. nigra kernels are also produced commercially in the US.

Two-thirds of the world export market[citation needed][how?][8][9] and 99% of US walnuts are grown in California's Central Valley and in Coastal Valleys, from Redding in the north to Bakersfield in the south.[10] Of the more than 30 varieties of J. regia grown there, Chandler and Hartley account for over half of total production.[9] In California commercial production, the Hinds' black walnut (J. hindsii) and the hybrid between J. hindsii and J. regia, Juglans x paradox, are widely used as rootstocks for J. regia cultivars because of their resistance to Phytophthora and to a very limited degree, the oak root fungus. However, trees grafted on these rootstocks often succumb to black line.[11]

In some countries, immature nuts in their husks are preserved in vinegar. In the UK, these are called pickled walnuts and this is one of the major uses for fresh nuts from the small scale plantings. In Armenian cuisine, unripe walnuts, including husks, are preserved in sugar syrup and eaten whole. In Italy, liqueurs called Nocino and Nocello are flavoured with walnuts, while Salsa di Noci (walnut sauce) is a pasta sauce originating from Liguria. In Georgia, walnuts are ground with other ingredients to make walnut sauce.

Green leaves of a walnut tree with budding walnuts, in Kashmir Valley.

Walnuts are heavily used in India. In Jammu, it is used widely as a prasad (offering) to Mother Goddess Vaisnav Devi and, generally, as a dry food in the season of festivals such as Diwali.

The nuts are rich in oil, and are widely eaten both fresh and in cookery. Walnut oil is expensive and consequently is used sparingly; most often in salad dressings. Walnut oil has been used in oil paint, as an effective binding medium, known for its clear, glossy consistency and nontoxicity.

Manos and Stone studied the composition of seed oils from several species of the Rhoipteleaceae and Juglandaceae and found the nut oils were generally more unsaturated from species which grow in the temperate zones and more saturated for species which grow in the tropical zones.[12] In the northerly-growing section Trachycaryon, J. cinerea oil was reported to contain 15% linolenate (the report did not specify whether the linolenate was the alpha (n-3) or gamma (n-6) isomer, or perhaps a mixture), 2% of saturated palmitate, and a maximum concentration of 71% linoleate. In the section Juglans, J. regia nut oil was found to contain from 10% to 11% linolenate, 6% to 7% palmitate, and a maximum concentration of linoleate (62% to 68%). In the section Cardiocaryon, the nut oils of J. ailantifolia and J. mandshurica were reported to contain (respectively) 7% and 5% of linolenate, 2% of palmitate, and maximum concentrations of 74% and 79% linoleate. Within the section Rhysocaryon, the nut oils of the U.S. native black walnuts J. microcarpa and J. nigra were reported to contain (respectively) 7% and 3% linolenate, 4% and 3% palmitate, and 70% and 69% linoleate. The remaining results for black walnuts were: J. australis contained 2% linolenate, 7% palmitate, and 61% linoleate; J. boliviana contained 4% linolenate, 4% palmitate, and 70% linoleate; J. hirsuta contained 2% linolenate, 5% palmitate, and 75% linoleate; J. mollis contained 0% linolenate, 5% palmitate, 46% linoleate, and 49% oleate; J. neotropica contained 3% linolenate, 5% palmitate, and 50% linoleate; and J. olanchana contained only a trace of linolenate, 9% palmitate, and 73% linoleate;


The shells of walnuts

The walnut shell has a wide variety of uses. Eastern black walnut (J. nigra) shell is the hardest of the walnut shells, and therefore has the highest resistance to breakdown.

Cleansing and polishing
Walnut shells are mostly used to clean soft metals, fiberglass, plastics, wood and stone. This environmentally friendly and recyclable soft grit abrasive is well suited for air blasting, deburring, descaling, and polishing operations because of its elasticity and resilience. Uses include cleaning automobile and jet engines, electronic circuit boards, and paint and graffiti removal. For example: In the early days of jet transportation, crushed walnut shells were used to scour the compressor airfoils clean, but when engines with air cooled vanes and blades in the turbine started being manufactured, this practice was stopped because the crushed shells tended to plug up the cooling passages to the turbine, resulting in turbine failures due to overheating.
Oil well drilling
The shell is used widely in oil well drilling for lost circulation material in making and maintaining seals in fracture zones and unconsolidated formations.
Flour from walnut shells can be used in thermoplastic starch composites to substitute oil derivatives.[13]
Paint thickener
Walnut shells are added to paint to give it a thicker consistency for "plaster effect" ranges.
Used as a filler in dynamite
Cosmetic cleaner
Occasionally used in soap and exfoliating cleansers


Staining from handling walnuts with husks

Walnut husks are often used to create a rich yellow-brown to dark brown dye used for dyeing fabric, yarn or wood and for other purposes. The dye does not require a mordant and will readily stain the hand if picked without gloves.


Walnut shoot cut longitudinally to show chambered pith, scale in mm

The common walnut, and the black walnut and its allies, are important for their attractive timber, which is hard, dense, tight-grained and polishes to a very smooth finish. The color is dark chocolate or similar in the heartwood changing by a sharp boundary to creamy white in the sapwood. When kiln-dried, walnut wood tends toward a dull brown color, but when air-dried can become a rich purplish-brown. Because of its color, hardness and grain, it is a prized furniture and carving wood.

When walnut vascular cambium is involved in a crotch (a branch fork), it behaves unusually, producing characteristic "crotch figure" in the wood which it makes. The grain figure exposed when a crotch in a walnut log is cut in the plane of its one entering branch and two exiting branches is attractive and sought after.

There are some differences between the wood of the European walnut (Juglans regia) and the wood of the black walnut (Juglans nigra). For example, Juglans regia wood sometimes has patches with a wavy texture.[14] Black walnut wood tends to be darker than European walnut wood, and can suffer from paler sapwood that only really comes to light when the wood has been planed.

Walnut wood has been the timber of choice for gun makers for centuries, including the Gewehr 98 and Lee–Enfield rifles of the First World War. It remains one of the most popular choices for rifle and shotgun stocks, and is generally considered to be the premium – as well as the most traditional – wood for gun stocks, due to its resilience to compression along the grain. Walnut is also used in lutherie and for the body of pipe organs.

Walnut burls (or "burrs" in the rest of the world) are commonly used to create bowls and other turned pieces. Walnut burl veneer is one of the most valuable and highly prized by cabinet makers and prestige car manufacturers.

The wood of the butternut and related Asian species is of much lower value, softer, coarser, less strong and heavy, and paler in colour.

Freshly sawn walnut heartwood may be greenish in color, but with exposure to air this color quickly changes to brown due to oxidation of the pigment.

In North America, forestry research has been undertaken, mostly on J. nigra, aiming to improve the quality of planting stock and markets. In some areas of the US, black walnut is the most valuable commercial timber species.[15] The Walnut Council[16] is the key body linking growers with scientists. In Europe, various EU-led scientific programmes have studied walnut growing for timber.[17]

The Cherokee Indians would produce a black dye from walnut bark, which they used to dye cloth.[18] As early as the 2nd century CE, shells and kernels of the edible walnut were used to make a dye solution in the Levant.[19][20]

Parkland and garden trees

Walnuts are very attractive trees in parks and large gardens. Walnut trees are easily propagated from the nuts. Seedlings grow rapidly on good soils.[15] The Japanese walnut in particular is known for its huge leaves, which have a tropical appearance.

Walnut tree in a garden

As garden trees, they have some drawbacks, in particular the falling nuts, and the releasing of the allelopathic compound juglone, though a number of gardeners do grow them.[21][22] However, different walnut species vary in the amount of juglone they release from the roots and fallen leaves - J. nigra, in particular, is known for its toxicity, both to plants and horses.[23] Juglone is toxic to plants such as tomato, apple, and birch, and may cause stunting and death of nearby vegetation. Juglone appears to be one of the walnut's primary defence mechanisms against potential competitors for resources (water, nutrients and sunlight), and its effects are felt most strongly inside the tree's "drip line" (the circle around the tree marked by the horizontal distance of its outermost branches). However, even plants at a seemingly great distance outside the drip line can be affected, and juglone can linger in the soil for several years even after a walnut is removed as its roots slowly decompose and release juglone into the soil.

Walnut as wildlife food plants

Walnut species are used as food plants by the larvae of some Lepidoptera species. These include[citation needed]:

The nuts are consumed by other animals, such as mice and squirrels.

In California (US) and Switzerland, crows have been witnessed taking walnuts into their beaks, flying up to 60 feet or so in the air, and dropping them to the ground to crack the shells and eat the nut inside.[24]

Nutritional information

The raw edible seed of walnut is composed of 4% water, 14% carbohydrates, 15% protein, and 65% fat.[25] In a 100 gram amount, walnuts provide 654 calories and are a rich source (≥20% of Daily Value) of protein, dietary fiber, the B vitamins, niacin, vitamin B6, and folate, and several dietary minerals, particularly manganese.[25]

Walnut oil is composed mostly of polyunsaturated fatty acids, particularly alpha-linolenic acid and linoleic acid, although it also contains oleic acid, a monounsaturated fat and 31% of total fat is saturated fat.[25]



The genus Juglans is divided into four sections.[26]

Sections and species

Section Description Image Name Common Name Subspecies Distribution
Section Cardiocaryon Leaves are very large (40–90 cm), with 11–19 broad leaflets, softly downy, margins serrated. The wood is soft, and the fruits borne in racemes of up to 20. The nuts have thick shells. Native to northeast Asia. J. ailantifolia Carr. (J. cordiformis Maxim., J. sieboldiana Maxim.) Japanese walnut Japan and Sakhalin
J. mandshurica Maxim. (J. cathayensis Dode, J. formosana Hayata, J. hopeiensis Dode, J. stenocarpa Maxim.) Manchurian walnut or Chinese walnut China, Russian Far East, Korea
Section Juglans Leaves are large (20–45 cm), with 5–9 broad leaflets, hairless, margins entire. The wood is hard. Native to southeast Europe to central Asia. J. regia L. (J. duclouxiana Dode, J. fallax Dode, J. orientis Dode) common walnut, Persian, English, or Carpathian walnut Balkans eastward to Himalaya, China
J. sigillata Dode iron walnut (doubtfully distinct from J. regia) China
Section Rhysocaryon (black walnuts) Leaves are large (20–50 cm), with 11–23 slender leaflets, finely pubescent, margins serrated. Native to North America and South America. J. australis Griseb. (J. brasiliensis Dode) Argentine walnut, Brazilian walnut Argentina, Bolivia
J. boliviana (C. DC.) Dode Bolivian walnut, Peruvian walnut Andes of Bolivia and Peru
J. californica S.Wats. California black walnut California
J. hindsii (Jepson) R.E.Smith Hinds' black walnut California
J. hirsuta Manning Nuevo León walnut Mexico
J. jamaicensis C.DC. (J. insularis Griseb.) West Indies walnut Cuba, the Dominican Republic, Haiti, and Puerto Rico
J. major (Torrey) Heller (J. arizonica Dode, J. elaeopyron Dode, J. torreyi Dode) Arizona black walnut
  • J. major var. glabrata Manning
Mexico, United States
J. microcarpa Berlandier (J. rupestris Engelm.) Texas black walnut
  • J. microcarpa var. microcarpa
  • J. microcarpa var. stewartii (Johnston) Manning
United States
J. mollis Engelm. Mexican walnut Mexico
J. neotropica Diels (J. honorei Dode) Andean walnut, cedro negro, cedro nogal, nogal, nogal Bogotano Colombia, Ecuador, and Peru
J. nigra L. Eastern black walnut Canada, United States
J. olanchana Standl. & L.O.Williams cedro negro, nogal, walnut
  • J. olanchana var. olanchana
  • J. olanchana var. standleyi
Central America, Mexico
J. soratensis Manning Bolivia
J. steyermarkii Manning Guatemalan walnut Guatemala
J. venezuelensis Manning Venezuelan walnut Venezuela
Section Trachycaryon Leaves are very large (40–90 cm), with 11–19 broad leaflets, softly downy, margins serrated. The wood is soft. Fruits are borne in clusters of two to three. The nuts have a thick, rough shell bearing distinct, sharp ridges. Native to eastern North America. J. cinerea L. Butternut Canada, United States

The best-known member of the genus is the Persian walnut (J. regia, literally "royal walnut"), native from the Balkans in southeast Europe, southwest and central Asia to the Himalaya and southwest China. Walnuts are a traditional feature of Iranian cuisine; the nation has extensive orchards which are an important feature of regional economies. In Kyrgyzstan alone, there are 230,700 ha of walnut-fruit forest, where J. regia is the dominant overstory tree (Hemery and Popov 1998). In non-European English-speaking nations, the nut of the J. regia is often called the "English walnut"; in Great Britain, the "common walnut."

The eastern black walnut (J. nigra) is a common species in its native eastern North America, and is also widely cultivated elsewhere. The nuts are edible, and though they are often used in expensive baked goods, the Persian walnut is preferred for everyday use because it is easier to extract the nutmeat. The wood is particularly valuable.

The Hinds' black walnut (J. hindsii) is native to northern California, where it has been widely used commercially as a rootstock for J. regia trees. Hinds' black walnut shells do not have the deep grooves characteristic of the eastern black walnut.

Japanese walnut foliage and nuts

The Japanese walnut (J. ailantifolia) is similar to butternut, distinguished by the larger leaves up to 90 cm long, and round (not oval) nuts. The variety cordiformis, often called the heartnut has heart-shaped nuts; the common name of this variety is the source of the sectional name Cardiocaryon.

The butternut (J. cinerea) is also native to eastern North America, where it is currently endangered by an introduced disease, butternut canker, caused by the fungus Sirococcus clavigignenti-juglandacearum. Its leaves are 40–60 cm long, the fruits are oval, the shell has very tall, very slender ridges, and the kernel is especially high in fat.



A study[27] of sequenced nuclear DNA from the external transcribed spacer (ETS) of ribosomal DNA (rDNA), the internal transcribed spacer (ITS) of rDNA, and the second intron of the LEAFY gene taken from at least one individual of most of the species of Juglans has supported several conclusions:

The paper presenting these results did not publish any new names for the subdivisions of sect. Rhysocaryon, for any combinations of the other sections, or for J. olanchana var. standleyi.

Paleontological history

Fossils of Juglans nuts have been described from the Tertiary period of North America.[28] The paleontological history of Juglans regia in Europe shows signs of a post-Ice-Age re-expansíon from refugia in the southeast, much influenced by people carrying walnut nuts about after the numbers of humans had been much increased by the start of agriculture.[citation needed]

See also


  1. ^ "Tropicos | Name - Juglans L." www.tropicos.org. Retrieved 29 June 2016.
  2. ^ "walnut". The American Heritage Dictionary of the English Language. Houghton Mifflin. Retrieved 10 February 2014.
  3. ^ "Online Etymology Dictionary". Etymonline.com. Retrieved 2015-07-16.
  4. ^ Ursula Buchan (4 October 2003). "Beat them as hard as you can". The Daily Telegraph. Archived from the original on 2022-01-12.
  5. ^ "Crops/Regions/World list/Production Quantity (pick lists), Walnuts (in shell), 2017". UN Food and Agriculture Organization, Corporate Statistical Database (FAOSTAT). 2019. Retrieved 11 October 2019.
  6. ^ "Fruit and Nut Trees – Fruit Bearing Plants " Blog Archive " Walnut Tree - Juglans regia – Juglans nigra". Fruitandnuttrees.com. Archived from the original on 2009-04-30. Retrieved 2015-07-16.
  7. ^ J. Derek Bewley; Michael Black; Peter Halmer (2006). The Encyclopedia of Seeds: Science, Technology and Uses. CABI. p. 250. ISBN 9780851997230.
  8. ^ "Walnuts" (PDF). USDA. Archived from the original (PDF) on October 18, 2012. Retrieved 2015-07-16.
  9. ^ a b "California Walnut History, Cultivation & Processing | California Walnuts". www.walnuts.org. Archived from the original on August 3, 2009.
  10. ^ "Frequently Asked Questions | California Walnuts". www.walnuts.org. Archived from the original on August 26, 2009.
  11. ^ www.padil.gov.au https://web.archive.org/web/20120906054734/http://www.padil.gov.au/viewPestDiagnosticImages.aspx?id=601. Archived from the original on September 6, 2012. ((cite web)): Missing or empty |title= (help)
  12. ^ Manos, Paul S. and Stone, Donald E.: "Phylogeny and Systematics of the Juglandaceae" Annals of the Missouri Botanical Garden 88(2)231–269 Spring, 2001
  13. ^ "Physical and mechanical properties of walnut shell flour-filled thermoplastic starch composites :: BioResources".
  14. ^ Youtube video CURLY WALNUT BEAUTY !!! WOW !!!
  15. ^ a b "Arquivo.pt". Archived from the original on 2009-07-08. Retrieved 2017-04-07.((cite web)): CS1 maint: bot: original URL status unknown (link)
  16. ^ "Walnut Council--Growing Walnut and Other Fine Hardwoods". Walnutcouncil.org. Retrieved 2015-07-16.
  17. ^ "BBC Radio 4 - Open Country". Bbc.co.uk. Retrieved 2015-07-16.
  18. ^ Knight, Oliver (1956–57), "History of the Cherokees, 1830–1846", Chronicles of Oklahoma, Oklahoma City: Oklahoma Historical Society, p. 164, OCLC 647927893
  19. ^ Mishnah (Shevi'it 7:3 [p. 47])
  20. ^ Foreman, Grant (1934). The Five Civilized Tribes. Norman: University of Oklahoma Press. pp. 283–284. ISBN 978-0-8061-0923-7.
  21. ^ Ross (1996)
  22. ^ www.wvu.edu https://web.archive.org/web/20150212041801/http://www.wvu.edu/~agexten/hortcult/fruits/blkwalnt.htm. Archived from the original on February 12, 2015. ((cite web)): Missing or empty |title= (help)
  23. ^ Rood (2001); Pomogaybin et al. (2002)
  24. ^ Cristol, Daniel A.; Switzer, Paul V. (1 May 1999). "Avian prey-dropping behavior. II. American crows and walnuts". Behavioral Ecology. 10 (3): 220–226. doi:10.1093/beheco/10.3.220.
  25. ^ a b c "Nutrition facts: Nuts, walnuts, English, per 100 g". Condé Nast for the US Department of Agriculture National Nutrient Database, Standard Release 21. 2014. Retrieved 4 July 2014.
  26. ^ Aradhya, M. K., D. Potter, F. Gao, C. J. Simon: "Molecular phylogeny of Juglans (Juglandaceae): a biogeographic perspective",Tree Genetics & Genomes(2007)3:363–378
  27. ^ D. Stone, S. Oh, E. Tripp, Luis. Gios, P. Manos: "Natural history, distribution, phylogenetic relationships, and conservation of Central American black walnuts (Juglans sect. Rhysocaryon)", Journal of the Torrey Botanical Society 136(1)1–25. 2009.
  28. ^ McNair, Daniel; Stults, Debra Z.; Axsmith, Brian; Alford, Mac H.; Starnes, James E. (July 2019). "Miocene Plants of Mississippi". Palaeontologia Electronica. 22 (2): 1–29. doi:10.26879/906. S2CID 198410494.