Juglans (Walnut trees)
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.
Etymology
The common name walnut derives from Old English wealhhnutu, literally 'foreign nut' (from wealh 'foreign' + hnutu 'nut'),because it was introduced from Gaul and Italy. The Latin name for the walnut was nux Gallica, "Gallic nut".
The genericomes name c from Latin jūglans, meaning 'walnut, walnut tree'; jūglans in turn is a contraction of Jōvis glans, 'nut of [the god] Jupiter'.
Folklore
Tradition has it that a walnut tree should be beaten. This would have the benefit of removing dead wood and stimulating shoot formation.
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 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.
Flowers
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.
Fruit
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.
Nuts and kernels
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 marketand 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.Of the more than 30 varieties of J. regia grown there, Chandler and Hartley account for over half of total production.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.
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.
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. 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;
Shells
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 made from walnut shells is widely used in the plastics industry.
- 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
Husks
Walnut husks are often used to create a rich yellow-brown to dark brown dye used for dyeing fabric and for other purposes. The dye does not require a mordant and will readily stain the hand if picked without gloves.
Wood
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 colour ranges from creamy white in the sapwood to a dark chocolate 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 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. 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, 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.The Walnut Councilis the key body linking growers with scientists. In Europe, various EU-led scientific programmes have studied walnut growing for timber.
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.The Japanese walnut in particular is known for its huge leaves, which have a tropical appearance.
Walnut as wildlife food plants
Walnuts are used as food plants by the larvae of some Lepidoptera species. These include:
- Brown-tail (Euproctis chrysorrhoea)
- Coleophora case-bearers C. laticornella (recorded on J. nigra) and C. pruniella.
- Common emerald (Hemithea aestivaria)
- Emperor moth (Pavonia pavonia)
- The engrailed (Ectropis crepuscularia)
- Walnut sphinx (Amorpha juglandis)
- Bride (Catocala neogama) – nominate subspecies on butternut and others, C. n. euphemia on Arizona black walnut, perhaps Texas black walnut and others.
The nuts are consumed by other animals, such as mice and squirrels.
In California (US) and Geneva (Switzerland), ravens 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.[citation needed]
Nutritional information
The raw edible seed of walnut is composed of 4% water, 14% carbohydrates, 15% protein, and 65% fat.In a 100 gram amount, walnuts provide 654 calories and are a rich source (20% or more of the Daily Value) of protein, dietary fiber, the B vitamins, niacin, vitamin B6, and folate, and several dietary minerals, particularly manganese.
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.
en.wikipedia.org
https://en.wikipedia.org/wiki/Juglans
Continue reading