Walnut - Juglans

Walnuts (genus Juglans) are plants in the family Juglandaceae. They are deciduous trees, 10 - 40 meters tall (about 30-130 ft.), with pinnate leaves 200 - 900 millimetres long (about 7-35 inches), with 5 - 25 leaflets.

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.


Cultivation and uses
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.

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.

In 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.

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.

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.

A 2006 study published in the Journal of the American College of Cardiology found that eating walnuts after a meal high in unhealthy fats can reduce the damaging effects of such fats on blood vessels. Researchers from Barcelona's Hospital Clinic conducted a study on 24 adult participants, half of whom had normal cholesterol levels, and half of whom had moderately high levels of cholesterol. Each group was fed two high-fat meals of salami and cheese, eaten one week apart. During one meal, the researchers supplemented the food with five teaspoons of olive oil. The researcher added eight shelled walnuts to the other meal, the following week.

Tests after each meal showed that both the olive oil and the walnuts helped reduce the onset of dangerous inflammation and oxidation in the arteries after the meals, which were high in saturated fat. However, unlike the olive oil, the walnuts also helped the arteries maintain their elasticity and flexibility, even in the participants with higher cholesterol.

In Traditional Chinese Medicine, walnut seeds are primarily considered a kidney tonic. They are also considered beneficial to the brain, back, and skin, and to relieve constipation if it is caused by dehydration.


Species
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 (Hemery 1998)—notably at Arslanbob in Jalal-Abad Province.
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.

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. 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.

Juglans nigra, commonly known as black walnut or American walnut, is a tree species native to eastern North America. It grows mostly alongside rivers, from southern Ontario, Canada west to southeast South Dakota, south to Georgia, northern Florida and southwest to central Texas. The Black Walnut was introduced into Europe in 1629. It is cultivated there as a forest tree for its high quality wood. It is more resistant to frost than the Persian Walnut, but thrives best in the warmer regions of Europe of fertile, lowland soils with a high water table. It is a light-demanding species. The wood is used to make furniture and rifle stocks, and oil is pressed from the seeds.

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