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Walnut Definition
Courtesy Wiki
Juglans is a plant genus of the family Juglandaceae, the seeds of which are known as walnuts. They are deciduous trees, 10–40 meters tall (about 30–130 ft), with pinnate leaves 200–900 millimetres long (7–35 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.
Contents [hide] [edit] Etymology The trivial name 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).[1] The walnut was so called because it was introduced from Gaul and Italy. The Latin name for the walnut was nux Gallica, "Gallic nut".[1] The Linnaean name, Juglans (Latin iūglāns, -andis), is etymologically *dyew-*glandi- "Jove's acorn" (Proto-Indoeuropean *dyew- "sky, sky god", cf. Greek Zeus, Latin Iūpiter "sky-father"): figuratively, an acorn fit for a god.[citation needed]
[edit] Systematics [edit] Taxonomy The genus Juglans is divided into four sections.[2]
[edit] Sections and species
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. 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.
[edit] Hybrids
[edit] Cultivation and uses Walnut output in 2005 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.
[edit] 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 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.[4]
[edit] Fruit Some fruits are borderline and difficult to categorize. Hickory nuts (Carya) and walnuts (Juglans) in the Juglandaceae family grow within an outer husk; these fruits are technically drupes or drupaceous nuts, and thus not true botanical nuts. "Tryma" is a specialized term for such nut-like drupes.[5][6]
[edit] 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[7][8] and 99% of the US commercial production of English walnuts is grown in California's Central Valley and in Coastal Valleys, from Redding in the north to Bakersfield in the south.[9] Of the more than 30 varieties of J. regia grown there, Chandler and Hartley account for over half of total production.[10] 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, walnuts 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.[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;
[edit] 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.
The shells of walnuts
[edit] Wood 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 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 Gewehr 98 and Lee Enfield rifles of the First World War. It remains one 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. 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.[13] The Walnut Council is the key body linking growers with scientists. In Europe, various EU-led scientific programs have studied walnut growing for timber.[14]
Juglans is a plant genus of the family Juglandaceae, the seeds of which are known as walnuts. They are deciduous trees, 10–40 meters tall (about 30–130 ft), with pinnate leaves 200–900 millimetres long (7–35 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.
Contents [hide] [edit] Etymology The trivial name 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).[1] The walnut was so called because it was introduced from Gaul and Italy. The Latin name for the walnut was nux Gallica, "Gallic nut".[1] The Linnaean name, Juglans (Latin iūglāns, -andis), is etymologically *dyew-*glandi- "Jove's acorn" (Proto-Indoeuropean *dyew- "sky, sky god", cf. Greek Zeus, Latin Iūpiter "sky-father"): figuratively, an acorn fit for a god.[citation needed]
[edit] Systematics [edit] Taxonomy The genus Juglans is divided into four sections.[2]
[edit] Sections and species
- Juglans sect. 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. The origin is in northeast Asia.
- J. ailantifolia Carr. (J. cordiformis Maxim., J. sieboldiana Maxim.)—Japanese walnut
- J. ailantifolia var. cordiformis—Heartnut
- J. mandshurica Maxim. (J. cathayensis Dode, J. formosana Hayata, J. hopeiensis Dode, J. stenocarpa Maxim.)—Manchurian walnut or Chinese walnut
- J. ailantifolia Carr. (J. cordiformis Maxim., J. sieboldiana Maxim.)—Japanese walnut
- Juglans sect. Juglans. Leaves are large (20–45 cm), with 5–9 broad leaflets, hairless, margins entire. The wood hard. The origin is southeast Europe to central Asia.
- J. regia L. (J. duclouxiana Dode, J. fallax Dode, J. orientis Dode)—common walnut, Persian, English, or Carpathian walnut
- J. sigillata Dode—iron walnut (doubtfully distinct from J. regia)
- Juglans sect. Rhysocaryon (black walnuts) Leaves are large (20–50 cm), with 11–23 slender leaflets, finely pubescent, margins serrated. The wood is hard, but can be extremely hard (Brazilian walnut Janka hardness test of 3684). The origins are North America and South America.
- J. australis Griseb. (J. brasiliensis Dode)—Argentine walnut, Brazilian walnut
- J. boliviana (C. DC.) Dode—Bolivian walnut, Peruvian walnut
- J. californica S.Wats.—California black walnut
- J. hindsii (Jepson) R.E.Smith—Hinds' black walnut
- J. hirsuta Manning—Nuevo León walnut
- J. jamaicensis C.DC. (J. insularis Griseb.)—West Indies walnut
- J. major (Torrey) Heller (J. arizonica Dode, J. elaeopyron Dode, J. torreyi Dode)—Arizona black walnut
- J. major var. glabrata Manning
- J. microcarpa Berlandier (J. rupestris Engelm.)—Texas walnut or little black walnut
- J. microcarpa var. microcarpa
- J. microcarpa var. stewartii (Johnston) Manning
- J. mollis Engelm.--Mexican walnut
- J. neotropica Diels (J. honorei Dode)—Andean walnut, cedro negro, cedro nogal, nogal, nogal Bogotano
- J. nigra L.—Eastern black walnut
- J. olanchana Standl. & L.O.Williams--cedro negro, nogal, walnut
- J. olanchana var. olanchana
- J. olanchana var. standleyi
- J. peruviana Dode—Peruvian walnut
- J. soratensis Manning
- J. steyermarkii Manning--Guatemalan walnut
- J. venezuelensis Manning—Venezuela walnut
- Juglans sect. 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. Origin is in eastern North America.
- J. cinerea L.—Butternut
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. 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.
[edit] Hybrids
- J. × bixbyi Rehd.--J. ailantifolia x J. cinerea
- J. × intermedia Carr.--J. nigra x J. regia
- J. × notha Rehd.--J. ailantifolia x J. regia
- J. × quadrangulata (Carr.) Rehd.--J. cinerea x J. regia
- J. × sinensis (D. C.) Rehd.--J. mandschurica x J. regia
- J. × paradox Burbank--J. hindsii x J. regia
- J. × royal Burbank--J. hindsii x J. nigra
- The genus Juglans is monophyletic;
- Sect. Cardiocaryon is sister to Sect. Trachycaryon;
- Sect. Juglans is sister to Sect. Cardiocaryon and Sect. Trachycaryon together;
- Sect. Rhysocaryon is monophyletic and sister to Sect. Juglans, Sect. Cardiocaryon, and Sect. Trachycaryon together;
- Sect. Rhysocaryon, the black walnuts, contains two clades:
- one comprises the more northerly species J. californica, J. hindsii, J. hirsuta, J. major, J. microcarpa, and J. nigra;
- the other comprises the more southerly species J. australis, J. boliviana, J. jamaicensis, J. molis, J. neotropica, J. olanchana, J. steyermarkii, and J. venezuelensis
- J. olanchana var. standleyi seems to be more closely related to J. steyermarkii than to J. olanchana var. olanchana, suggesting J. olanchana var. standleyi might be better understood as either a separate species or a variety of J. steyermarkii.
[edit] Cultivation and uses Walnut output in 2005 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.
[edit] 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 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.[4]
[edit] Fruit Some fruits are borderline and difficult to categorize. Hickory nuts (Carya) and walnuts (Juglans) in the Juglandaceae family grow within an outer husk; these fruits are technically drupes or drupaceous nuts, and thus not true botanical nuts. "Tryma" is a specialized term for such nut-like drupes.[5][6]
[edit] 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[7][8] and 99% of the US commercial production of English walnuts is grown in California's Central Valley and in Coastal Valleys, from Redding in the north to Bakersfield in the south.[9] Of the more than 30 varieties of J. regia grown there, Chandler and Hartley account for over half of total production.[10] 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, walnuts 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.[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;
[edit] 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.
The shells of walnuts
- 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
[edit] Wood 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 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 Gewehr 98 and Lee Enfield rifles of the First World War. It remains one 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. 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.[13] The Walnut Council is the key body linking growers with scientists. In Europe, various EU-led scientific programs have studied walnut growing for timber.[14]