WALNUT TREE
Walnut Tree (genus Juglans) are plants in the family Juglandaceae.
They are deciduous trees, 10 - 40 metres tall (about 30-130 ft.), with pinnate leaves 200 - 900 millimetres long (about 7-35 inches), 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.
The Latin name Juglans derives from Jovis glans, "Jupiter's acorn": figuratively, a nut fit for a god.
The word walnut derives from Old English wealhhnutu, literally "foreign nut", wealh meaning "foreign" (wealh is akin to the terms Welsh and Vlach; see *Walha and History of the term Vlach).
The walnut was so called because it was introduced from Gaul and Italy. The previous Latin name for the walnut was nux Gallica, "Gallic nut".
Species and classification of the Walnut Tree:
Sect. Juglans. Leaves large (20-45 cm) with 5-9 broad leaflets, hairless, margins entire. Wood hard. Southeast Europe to central Asia.
Juglans regia L. (J. duclouxiana Dode, J. fallax Dode, J. orientis Dode) - Persian Walnut, Carpathian, or Common Walnut
Juglans sigillata Dode - Iron Walnut (doubtfully distinct from J. regia)
Sect. Rhysocaryon. Leaves large (20-50 cm) with 11-23 slender leaflets, finely pubescent, margins serrated. Wood hard. North America, South America.
Juglans australis Griseb. (J. boliviana Dode) - Argentine Walnut
Juglans brasiliensis Dode - Brazilian Walnut
Juglans californica S.Wats. - California Walnut
Juglans hindsii (Jepson) R.E.Smith - Hinds' Walnut
Juglans hirsuta Manning - Nuevo Leon Walnut
Juglans jamaicensis C.DC. (J. insularis Griseb.) - West Indies Walnut
Juglans major (Torrey) Heller (J. arizonica Dode, J. elaeopyron Dode, J. torreyi Dode) - Arizona Walnut
Juglans major var. glabrata Manning
Juglans microcarpa Berlandier (J. rupestris Engelm.) - Texas Walnut or Little Walnut
Juglans microcarpa var. stewartii (Johnston) Manning
Juglans mollis Engelm. - Mexican Walnut
Juglans neotropica Diels (J. honorei Dode) - Andean Walnut
Juglans nigra L. - Black Walnut
Juglans olanchana Standl. & L.O.Williams -
Juglans peruviana Dode - Peruvian Walnut
Juglans soratensis Manning -
Juglans steyermarkii Manning - Guatemalan Walnut
Juglans venezuelensis Manning - Venezuela Walnut
Sect. Cardiocaryon. Leaves very large (40-90 cm) with 11-19 broad leaflets, softly downy, margins serrated. Wood soft. Northeast Asia, eastern North America.
Juglans ailantifolia Carr. (J. cordiformis Maxim., J. sieboldiana Maxim.) - Japanese Walnut
Juglans cinerea L. - Butternut
Juglans mandshurica Maxim. (J. cathayensis Dode, J. formosana Hayata, J. hopeiensis Dode, J. stenocarpa Maxim.) - Manchurian Walnut or Chinese Walnut.
The best-known member of the genus is the Persian Walnut (Juglans regia), native from the Balkans in southeast Europe, southwest & central Asia to the Himalaya and southwest China.
The scientific name Juglans is from the Latin jovis glans, "Jupiter's acorn", and regia, "royal". Its common name, Persian walnut, indicates its origins in Persia (Iran) in southwest Asia; 'walnut' derives from the Germanic wal- for "foreign", recognising that it is not a nut native to northern Europe.
The Black Walnut (Juglans nigra) is a common species in its native eastern North America, and is also widely cultivated elsewhere. The nuts are edible, but have a smaller kernel and an extremely tough shell, and they are not widely grown for nut production.
The Butternut (Juglans 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. Its leaves are 40-60 cm long, and the nuts oval.
The Japanese Walnut (Juglans ailantifolia) is similar to Butternut, distinguished by the larger leaves up to 90 cm long, and round (not oval) nuts.
Hybrids
Juglans x bixbyi Rehd. - J. ailantifolia x J. cinerea
Juglans x intermedia Carr. - J. nigra x J. regia
Juglans x notha Rehd. - J. ailantifolia x J. regia
Juglans x quadrangulata (Carr.) Rehd. - J. cinerea x J. regia
Juglans x sinensis (D. C.) Rehd. - J. mandschurica x J. regia
Juglans x paradox Burbank - J. hindsii x J. regia
Juglans x royal Burbank - J. hindsii x J. nigra.
Cultivation and uses of the Walnut Tree:
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 E. 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.
There are many different cultivars available for growers, offering different growth habit, flowering and leafing, kernel flavour and shell thickness. A key trait for more northerly latitudes of N. 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.
Nuts of the Walnut Tree:
The nuts of all the species are edible, but the walnuts commonly available in shops are from the Persian Walnut, the only species which has a large nut and thin shell.
A horticultural form selected for thin nut shells and hardiness in temperate zones is sometimes known as the 'Carpathian' walnut. 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 dressing.
Walnuts are also an excellent source of omega-3 fatty acids, and have been shown as helpful in lowering cholesterol. They need to be kept dry and refrigerated to store well; in warm conditions they become rancid in a few weeks, particularly after shelling.
Oil paint often employs walnut oil as an effective binding medium, known for its clear, glossy consistency and non-toxicity. Flour made from walnut shells is widely used in the plastics industry.
Persian WalnutsIn some countries immature nuts in their husks are preserved in vinegar. In England these are called "pickled walnuts" and this is one of the major uses for fresh nuts from the small scale plantings.
In Armenian cuisine, walnuts are preserved in sugar syrup and eaten whole. In Italy, liqueurs called Nocino and Nocello are flavoured with walnuts. In Georgia, walnuts are ground along with other ingredients to make walnut sauce.
Walnuts are heavily used in India.
In Jammu, India 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.
Walnut husks are often used to create a rich yellow-brown to dark brown dye that is used for dyeing fabric and for other purposes. When picking walnuts, the husks should be handled wearing rubber gloves, to avoid dyeing one's fingers.
Wood of the Walnut Tree:
The Persian 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 colour ranges from creamy white in the sapwood to a dark chocolate colour in the heartwood. When kiln-dried, walnut wood tends toward a dull brown colour, but when air-dried can become a rich purplish-brown.
Because of its colour, hardness and grain it is a prized furniture and carving wood. Walnut burls (or 'burrs' in Europe) are commonly used to create bowls and other turned pieces.
Veneer sliced from walnut burl is one of the most valuable and highly prized by cabinet makers and prestige car manufacturers. Walnut wood has been the timber of choice for gun makers for centuries, including the Lee Enfield rifle of the First World War.
Today it is used for exclusive sporting guns.
The wood of the Butternut and related Asian species is of much lower value, softer, coarser, less strong and heavy, and paler in colour.
In North America research has been undertaken mostly on Juglans nigra aiming to improve the quality of planting stock and markets. The Walnut Council is the key body linking growers with scientists. In Europe, various EU-led scientific programs have studied walnut growing for timber.
Shells of the Walnut Tree:
The walnut shell has a wide variety of uses. It is commonly used as an organic abrasive, to polish and clean a number of different materials. Black walnut shell is the hardest of the walnut shells, and therefore has the highest resistance to break-down.
It is environmentally friendly and can be recycled.
Cleansing and polishing: Walnut shells are mostly used to clean soft metals, fiberglass, plastics, wood and stone. Uses include cleaning automobile and jet engines, electronic circuit boards, and paint and grafitti removal.
This soft grit abrasive is well suited for air blasting, de-burring, de-scaling, and polishing operations because of its elasticity and resilience.
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.
Paint thickener: Walnut shells are added to paint to give it a thicker consistency for "plaster effect" ranges.
Explosives: Used as a filler in dynamite.
Cosmetic cleaner: Occasionally used in soap and exfoliating cleansers.
Parkland and garden trees of the Walnut Tree:
Walnuts are very attractive trees in parks and large gardens. The Japanese Walnut in particular is grown for its huge leaves, which have a 'tropical' appearance.
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.
The toxic effect of walnut trees was reported by Pliny.
owever, different walnut species vary in the amount of juglone they release from the roots and fallen leaves - the black walnut in particular is known for its toxicity.
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.
The Tree: A Natural History of What Trees Are, How They Live, and Why They Matter
Walnut as food plants:
Walnuts are a popular snack among woodland creatures, specifically mice and squirrels.
Juglans regia (the Common walnut, Persian walnut, or English walnut), is the original walnut tree of the Old World.
It is native in a 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.
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, with scattered broad fissures with a rougher texture. Like all walnuts, the pith of the twigs contains air spaces, the chambered pith brownish in colour.
The leaves are alternately arranged, 25-40 cm long, odd-pinnate with 5-9 leaflets, paired alternately with one terminal leaflet. The largest leaflets the three at the apex, 10-18 cm long and 6-8 cm broad; the basal pair of leaflets much smaller, 5-8 cm long, the margins of the leaflets entire.
The male flowers are in drooping catkins 5-10 cm long, the female flowers terminal, in clusters of two to five, ripening in the autumn into a fruit with a green, semi-fleshy 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.
The walnut was introduced into western and northern Europe very early, by Roman times or earlier, and to the Americas by the 17th century.
Important nut-growing regions include France, Serbia, Greece, Bulgaria, and Romania in Europe, China in Asia, California in North America, and Chile in South America.
It is cultivated extensively for its high-quality nuts, eaten both fresh and pressed for their richly flavoured oil; numerous cultivars have been selected for larger and thin-shelled nuts.
The wood is of very high quality, and is used to make furniture and rifle stocks.
Walnut ink, made by boiling the whole fruit or letting it oxidize, then releasing onto the exterior, is dark brown in color and darkens as it oxidizes. It can also be used to stain wood.
Nutritional value
100 g shelled walnuts provide:
15.2 g protein
65.2 g fat:
6.1 g saturated fat
8.9 g monounsaturated fat
47.2 g polyunsaturated fat
13.7 g carbohydrates, including 6.7 g dietary fiber
0.34 mg Thiamin
0.54 mg Vitamin B6
98 µg Folate
3.4 mg Manganese
1.6 mg Copper
158 mg Magnesium
346 mg Phosphorus
3.1 mg Zinc
The scientific name Juglans is from Latin jovis glans, "Jupiter's nut", and regia, "royal". Its common name, Persian walnut, indicates its origins in Persia in southwest Asia; 'walnut' derives from the Germanic wal- for "foreign", recognising that it is not a nut native to northern Europe.
Other names include Walnut (which does not distinguish the tree from other species of Juglans), Common Walnut and English Walnut, the latter name possibly because English sailors were prominent in Juglans regia nut distribution at one time.
Juglans sigillata, known as the Iron Walnut, is a species of walnut tree.
The tree has been cultivated for its edible nuts.
The nuts are oval-shaped with bumps and ridges. The tree is also use for its wood. It is commonly found in Yunnan, but are also found in Guizhou, Sichuan and Xizang in China.
It is sometimes grown in gardens and parks as an ornamental plant.
Ocotea porosa is a species of plant in the Lauraceae family, often placerd in the related genus Phoebe. Common names include Embuya, canella imbuia and "Brazilian Walnut" (it is not closely related to walnuts).
The tree is found in the subtropical montane Araucaria angustifolia rain forests of southern Brazil, mostly in the states of Paraná and Santa Catarina, and in smaller numbers in São Paulo and Rio Grande do Sul. The spoecies may also occur in adjacent Argentina and/or Paraguay.
At their largest, the trees may reach 40 meters in height and 1.8 meters in trunk diameter. The tree is a major commercial species in Brazil because of the value of its wood for high end furniture, mostly as decorative veneers, and as flooring.
The tree is a popular horticultural tree in subtropical regions of the world. In its native habitat it is a threatened species.
Juglans californica, the California Black Walnut, also called the California Walnut, or the Southern California Black Walnut, is a large shrub or small tree endemic to California. There are two known varieties (according to the The Jepson Manual) or subspecies (according to the California Native Plant Society).
The California black walnut can be either a large shrub with 1-5 trunks, or a small single-trunked tree. The main trunk can fork close to the ground making it look like two trees that have grown together, then diverged.
It can grow as tall as 25m and has thick bark, deeply channeled or furrowed at maturity. It has large, pinnately compound leaves with 11-19 lanceolate leaflets with toothed margins. It has a small hard nut in a shell that is difficult to remove.
The Chumash Indians of the Channel Islands of California eat the nuts, however, they are not grown commercially for this purpose.
The Northern California black walnut is commercially important as a rootstock for English walnut orchards all over the world, both on its own and as a parent to the J. hindsii x J. regia 'Paradox' hybrid.
In the walnut industry the Northern California black walnut variety is usually called Juglans hindsii, and the Southern California black walnut is called Juglans californica. The Northern California variety is endangered, with possibly only a few native stands remaining.
The Southern California variety is threatened by development and overgrazing, although there are far more native stands remaining, including some in urban Los Angeles.
The California black walnut grows in riparian woodlands, either in single species stands or mixed with California's oaks (Quercus) and cottonwoods (Populus).
It grows as part of mixed woodlands in California's Coast Ranges, Transverse Ranges, and Peninsular Ranges, and also on slopes and in valleys wherever conditions favor it throughout California west of the Sierra Nevada and the deserts and south of the Klamath Mountains.
It is cultivated as an ornamental tree wherever it will grow in California, and in Hawaii.
The Japanese Walnut is a species of walnut native to Japan and Sakhalin.
It is a deciduous tree growing to 20 m tall, rarely 30 m, and 40-80 cm stem diameter, with light grey bark.
The leaves are pinnate, 50-90 cm long, with 11-17 leaflets, each leaflet 7-16 cm long and 3-5 cm broad. The whole leaf is downy-pubescent, and a somewhat brighter, yellower green than many other tree leaves.
The flowers are inconspicuous yellow-green catkins produced in spring at the same time as the new leaves appear. The fruit is a nut, produced in bunches of 4-10 together; the nut is spherical, 3-5 cm long and broad, surrounded by a green husk before maturity in mid autumn.
The nuts have an oily texture. The husks are also used to make a yellowish dye.
The very bold, decorative leaves make it an excellent ornamental tree for planting in parks and large gardens.
Unlike the closely related and very similar North American Butternut, Japanese Walnut is resistant to the canker disease caused by the fungus Sirococcus clavigignenti-juglandacearum.
This has led to its being planted as a replacement for Butternuts in North America. The two species hybridise readily; the resulting hybrid Juglans x bixbyi is also resistant to canker and is likewise planted as a replacement for Butternuts.
Japanese Walnut is distinguished from Butternut by its larger leaves and round (not oval) nuts.
The wood is light and takes polish well, but is of much lower quality than Persian Walnut wood. It is often used to make furniture.
The Heartnut is a cultivar of Japanese Walnut distinguished by its fruit, which is heart-shaped in cross section, easier to crack, and able to yield an unbroken nut meat when cracked.
The Heartnut is a sweet nut without a bitter aftertaste often intrinsic with Black and Persian Walnuts.
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