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{{Taxobox
| color = lightgreen
| name = Walnut
| image = Walnut twig.jpg
| image_width = 250px
| image_caption = Shoot and nut of ''Juglans regia''
| regnum = [[Plant]]ae
| divisio = [[Flowering plant|Magnoliophyta]]
| classis = [[Dicotyledon|Magnoliopsida]]
| ordo = [[Fagales]]
| familia = [[Juglandaceae]]
| genus = '''''Juglans'''''
| genus_authority = [[Carolus Linnaeus|L.]]
| subdivision_ranks = Species
| subdivision = See text
}}
'''Walnuts''' (genus ''Juglans'') are [[plant]]s in the walnut family [[Juglandaceae]]. They are [[deciduous]] [[tree]]s, 10 - 40 [[metre]]s tall, with [[pinnate]] leaves 200 - 900 millimetres long, with 5 - 25 leaflets; the shoots have chambered [[pith]], a character shared with the [[wingnut]]s (''Pterocarya'') but not the [[hickory|hickories]] (''Carya'') in the same family.
[[Image:Walnut pith.jpg|250px|left|thumb|Walnut shoot cut longitudinally to show chambered [[pith]]. Scale in mm.]]
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 nuts", the nut fit for a god.
Walnuts are used as food plants by the [[larva]]e of some [[Lepidoptera]] species including [[Brown-tail]], [[Common Emerald]], [[Emperor Moth]], [[Engrailed|The Engrailed]] and the ''[[Coleophora]]'' case-bearers ''C. laticornella'' (recorded on ''J. nigra'') and ''C. pruniella''.
The word ''walnut'' derives from [[Old English language|Old English]] ''wealhhnutu'', literally "foreign nut", ''wealh'' meaning "foreign" (''wealh'' is akin to the terms [[Wiktionary:Welsh|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 Late [[Latin]] name for the walnut was ''nux Gallica'', "[[Gaul|Gallic]] nut".
==Species and classification==
*'''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]]
**''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 - [[Juglans hindsii|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 (tree)|Butternut]]
**''Jugl
ans mandschurica'' Maxim. (''J. cathayensis'' Dode, ''J. formosana'' Hayata, ''J. hopeiensis'' Dode, ''J. stenocarpa'' Maxim.) - [[Chinese Walnut]] or Manchurian Walnut
[[Image:Juglans ailantifolia.jpg|right|240px|thumb|Japanese Walnut foliage and nuts]]
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]]. In [[Kyrgyzstan]] alone there are 230,700 ha of walnut-fruit forest, where ''J. regia'' is the dominant overstorey (Hemery and Popov 1998). This is the species which is widely cultivated for its delicious [[nut (fruit)|nuts]]. ''J. regia'' is also called English walnut because English merchant marines once controlled its world commerce.
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 species|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==
The two most important species commercially are ''J. regia'' for timber and nuts, and ''J. nigra'' which is grown primarily for timber. Both species have similar cultivation requirements and are widely grown in temperate zones.
Walnuts are light-demanding species but benefit from protection from wind. Research has shown that interplanting walnut plantations with a [[nitrogen fixation|nitrogen fixing]] plant such as ''Elaeagnus × ebbingei'' or ''E. umbellata'', and various ''Alnus'' species can have a dramatic impact on tree height and girth, resulting in a 30% increase according to some studies (Hemery 2001).
When grown for nuts care must be taken to select [[cultivar]]s 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
[[Image:Walnut02.jpg|thumb|Persian Walnut nuts]]
[[Image:Walnut03.jpg|thumb|Inside of a Persian Walnut nut with green outer layer visible in the top left corner]]
[[Image:Walnuts02.jpg|thumb|Persian Walnuts]]
The [[nut (fruit)|nuts]] of all the species are edible, but the walnuts commonly available in stores 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 [[Walnut oil|oil]], and are widely eaten both fresh and in [[cookery]]. [[Oil paint]] often employs walnut oil as an effective binding medium, known for its clear, glossy consistency and non-toxicity
. 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.
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.
Walnut nut husks are often used to create a rich yellow-brown to dark brown [[dye]] that is used for dyeing [[textile|fabric]] and for other purposes. When picking walnuts, the husks should be handled wearing rubber gloves, to avoid dyeing one's fingers.
;Wood
The Persian Walnut, and the Black Walnut and its allies, are important for their attractive timber, which (except in young trees) is hard, dense, tight-grained and polishes to a very smooth finish. The color ranges from creamy white in the sapwood to a dark chocolate color in the heartwood. 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. 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 presitige car manufacturers. Walnut wood has been the timber of choice for gunmakers for centuries, including the [[Lee Enfield]] rifle of the First World War. Today it is used for exclusive sporting guns, by makers such as Purdy of London. The wood of the Butternut and related Asian species is of much lower value, softer, coarser, less strong and heavy, and paler in color.
In North America research has been undertaken mostly on ''Juglans nigra'' aiming to improve the quality of planting stock and markets. [http://www.walnutcouncil.org The Walnut Council] is the key body linking growers with scientists. In Europe, various EU-led scientific programs have studied walnut growing for timber (e.g. [http://www.bbc.co.uk/radio4/factual/opencountry_20020330.shtml in the UK]).
;Parkland and garden trees
Walnuts are very attractive trees in [[park]]s and large [[garden]]s. The Japanese Walnut in particular is grown for its huge leaves, which have a 'tropical' appearance.
Walnuts are not particularly well suited to smaller urban gardens. They drop numerous small twigs, leaves, branches or nuts, so are considered "messy" by some people; the falling nuts in late summer and early autumn can be quite dangerous. Both the fallen leaves and the roots secrete a substance called [[juglone]] which kills many popular garden plants, such as [[tomato]], [[apple]] and [[birch]]; all walnuts produce juglone, but Black Walnut produces larger amounts than other species. Juglone appears to be one of the walnut's primary defense 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 many years even after a walnut is removed as its roots slowly decompose and release juglone into the soil.
An old English rhyme states:
:A spaniel, a woman, and a walnut tree;
:The more they're beaten,
:The better still they be.
The meaning of this is the source of some debate, with three different takes on it given in the [http://www.bbc.co.uk/radio4/gqt/fsheets/02_02_03/fsheetsq8.shtml BBC's Gardeners' Question Time].
==Health benefits of walnuts==
[[Image:English Walnuts.jpg|thumb|250px|[[Juglans regia]] ''walnuts''.]]
A new 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 Ho
spital 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.
Lead researcher Dr. Emilio Ros said walnuts' protective effects could be because the nuts are high in antioxidants and ALA, a plant-based [[omega-3 fatty acid]]. Walnuts also contain [[arginine]], which is an amino acid that the body uses to produce nitric oxide, necessary for keeping blood vessels flexible.
Source: Journal of the American College of Cardiology - Oct. 17, 2006 edition
==Walnuts in the future==
Walnut species are deep rooted and already play an important role in slope stabilization, e.g. in the Himalaya. Some species may become more suited to northerly climes under a changing clmate, for example becoming more productive (timber and nuts)in the UK, and northerly US states. Their dark quality hardwood is potentially a valuable domestic timber for temperate areas and therefore an altenative source of tropical timbers such as [[Mahogany]]. Fast-grown hybrid walnut may produce a viable wood product for wood energy systems under [[Short Rotation Forestry]].
==References==
*[http://www.walnuts.org/walnuts101/index.php Informations about history, processing and health]
*[http://www.wvu.edu/~agexten/hortcult/fruits/blkwalnt.htm Juglone toxicity]
*[http://www.efloras.org/florataxon.aspx?flora_id=40&taxon_id=116860 Flora of Bolivia: ''Juglans'']
*[http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=116860 Flora of China: ''Juglans'']
*[http://rbg-web2.rbge.org.uk/cgi-bin/nph-readbtree.pl/feout?FAMILY_XREF=&GENUS_XREF=Juglans&SPECIES_XREF=&TAXON_NAME_XREF=&RANK= Flora Europaea: ''Juglans'']
*[http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=116860 Flora of North America: ''Juglans'']
*[http://www.efloras.org/florataxon.aspx?flora_id=5&taxon_id=116860 Flora of Pakistan: ''Juglans'']
*[http://www.efloras.org/florataxon.aspx?flora_id=201&taxon_id=116860 Trees of the Andes: ''Juglans'']
*[http://news.bbc.co.uk/2/hi/health/6036409.stm BBC article] lead to a reported 80% increase in demand at Waitrose. (ref. radio 4 news).
*[http://www.bbc.co.uk/radio4/factual/opencountry_20020330.shtml Walnut growing for timber research in the UK]
*Brinkman, K. A. (1974). Juglans L. - Walnut. In: Schopmeyer, C. S., ed. ''Seeds of woody plants in the United States''. Agriculture Handbook No. 450. Washington, DC: U.S. Department of Agriculture, Forest Service: 454-459.
*Hemery, G.E. and S.I. Popov, The walnut (Juglans regia L.) forests of Kyrgyzstan and their importance as a genetic resource. Commonwealth Forestry Review, 1998. 77(4): p. 272-276.
*Hemery, G. E. (2001). Growing walnut in mixed stands. ''Quart. J. Forestry'' 95: 31-36.
[[Category:Fagales]]
[[Category:Edible nuts and seeds]]
| color = lightgreen
| name = Walnut
| image = Walnut twig.jpg
| image_width = 250px
| image_caption = Shoot and nut of ''Juglans regia''
| regnum = [[Plant]]ae
| divisio = [[Flowering plant|Magnoliophyta]]
| classis = [[Dicotyledon|Magnoliopsida]]
| ordo = [[Fagales]]
| familia = [[Juglandaceae]]
| genus = '''''Juglans'''''
| genus_authority = [[Carolus Linnaeus|L.]]
| subdivision_ranks = Species
| subdivision = See text
}}
'''Walnuts''' (genus ''Juglans'') are [[plant]]s in the walnut family [[Juglandaceae]]. They are [[deciduous]] [[tree]]s, 10 - 40 [[metre]]s tall, with [[pinnate]] leaves 200 - 900 millimetres long, with 5 - 25 leaflets; the shoots have chambered [[pith]], a character shared with the [[wingnut]]s (''Pterocarya'') but not the [[hickory|hickories]] (''Carya'') in the same family.
[[Image:Walnut pith.jpg|250px|left|thumb|Walnut shoot cut longitudinally to show chambered [[pith]]. Scale in mm.]]
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 nuts", the nut fit for a god.
Walnuts are used as food plants by the [[larva]]e of some [[Lepidoptera]] species including [[Brown-tail]], [[Common Emerald]], [[Emperor Moth]], [[Engrailed|The Engrailed]] and the ''[[Coleophora]]'' case-bearers ''C. laticornella'' (recorded on ''J. nigra'') and ''C. pruniella''.
The word ''walnut'' derives from [[Old English language|Old English]] ''wealhhnutu'', literally "foreign nut", ''wealh'' meaning "foreign" (''wealh'' is akin to the terms [[Wiktionary:Welsh|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 Late [[Latin]] name for the walnut was ''nux Gallica'', "[[Gaul|Gallic]] nut".
==Species and classification==
*'''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]]
**''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 - [[Juglans hindsii|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 (tree)|Butternut]]
**''Jugl
ans mandschurica'' Maxim. (''J. cathayensis'' Dode, ''J. formosana'' Hayata, ''J. hopeiensis'' Dode, ''J. stenocarpa'' Maxim.) - [[Chinese Walnut]] or Manchurian Walnut
[[Image:Juglans ailantifolia.jpg|right|240px|thumb|Japanese Walnut foliage and nuts]]
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]]. In [[Kyrgyzstan]] alone there are 230,700 ha of walnut-fruit forest, where ''J. regia'' is the dominant overstorey (Hemery and Popov 1998). This is the species which is widely cultivated for its delicious [[nut (fruit)|nuts]]. ''J. regia'' is also called English walnut because English merchant marines once controlled its world commerce.
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 species|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==
The two most important species commercially are ''J. regia'' for timber and nuts, and ''J. nigra'' which is grown primarily for timber. Both species have similar cultivation requirements and are widely grown in temperate zones.
Walnuts are light-demanding species but benefit from protection from wind. Research has shown that interplanting walnut plantations with a [[nitrogen fixation|nitrogen fixing]] plant such as ''Elaeagnus × ebbingei'' or ''E. umbellata'', and various ''Alnus'' species can have a dramatic impact on tree height and girth, resulting in a 30% increase according to some studies (Hemery 2001).
When grown for nuts care must be taken to select [[cultivar]]s 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
[[Image:Walnut02.jpg|thumb|Persian Walnut nuts]]
[[Image:Walnut03.jpg|thumb|Inside of a Persian Walnut nut with green outer layer visible in the top left corner]]
[[Image:Walnuts02.jpg|thumb|Persian Walnuts]]
The [[nut (fruit)|nuts]] of all the species are edible, but the walnuts commonly available in stores 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 [[Walnut oil|oil]], and are widely eaten both fresh and in [[cookery]]. [[Oil paint]] often employs walnut oil as an effective binding medium, known for its clear, glossy consistency and non-toxicity
. 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.
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.
Walnut nut husks are often used to create a rich yellow-brown to dark brown [[dye]] that is used for dyeing [[textile|fabric]] and for other purposes. When picking walnuts, the husks should be handled wearing rubber gloves, to avoid dyeing one's fingers.
;Wood
The Persian Walnut, and the Black Walnut and its allies, are important for their attractive timber, which (except in young trees) is hard, dense, tight-grained and polishes to a very smooth finish. The color ranges from creamy white in the sapwood to a dark chocolate color in the heartwood. 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. 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 presitige car manufacturers. Walnut wood has been the timber of choice for gunmakers for centuries, including the [[Lee Enfield]] rifle of the First World War. Today it is used for exclusive sporting guns, by makers such as Purdy of London. The wood of the Butternut and related Asian species is of much lower value, softer, coarser, less strong and heavy, and paler in color.
In North America research has been undertaken mostly on ''Juglans nigra'' aiming to improve the quality of planting stock and markets. [http://www.walnutcouncil.org The Walnut Council] is the key body linking growers with scientists. In Europe, various EU-led scientific programs have studied walnut growing for timber (e.g. [http://www.bbc.co.uk/radio4/factual/opencountry_20020330.shtml in the UK]).
;Parkland and garden trees
Walnuts are very attractive trees in [[park]]s and large [[garden]]s. The Japanese Walnut in particular is grown for its huge leaves, which have a 'tropical' appearance.
Walnuts are not particularly well suited to smaller urban gardens. They drop numerous small twigs, leaves, branches or nuts, so are considered "messy" by some people; the falling nuts in late summer and early autumn can be quite dangerous. Both the fallen leaves and the roots secrete a substance called [[juglone]] which kills many popular garden plants, such as [[tomato]], [[apple]] and [[birch]]; all walnuts produce juglone, but Black Walnut produces larger amounts than other species. Juglone appears to be one of the walnut's primary defense 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 many years even after a walnut is removed as its roots slowly decompose and release juglone into the soil.
An old English rhyme states:
:A spaniel, a woman, and a walnut tree;
:The more they're beaten,
:The better still they be.
The meaning of this is the source of some debate, with three different takes on it given in the [http://www.bbc.co.uk/radio4/gqt/fsheets/02_02_03/fsheetsq8.shtml BBC's Gardeners' Question Time].
==Health benefits of walnuts==
[[Image:English Walnuts.jpg|thumb|250px|[[Juglans regia]] ''walnuts''.]]
A new 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 Ho
spital 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.
Lead researcher Dr. Emilio Ros said walnuts' protective effects could be because the nuts are high in antioxidants and ALA, a plant-based [[omega-3 fatty acid]]. Walnuts also contain [[arginine]], which is an amino acid that the body uses to produce nitric oxide, necessary for keeping blood vessels flexible.
Source: Journal of the American College of Cardiology - Oct. 17, 2006 edition
==Walnuts in the future==
Walnut species are deep rooted and already play an important role in slope stabilization, e.g. in the Himalaya. Some species may become more suited to northerly climes under a changing clmate, for example becoming more productive (timber and nuts)in the UK, and northerly US states. Their dark quality hardwood is potentially a valuable domestic timber for temperate areas and therefore an altenative source of tropical timbers such as [[Mahogany]]. Fast-grown hybrid walnut may produce a viable wood product for wood energy systems under [[Short Rotation Forestry]].
==References==
*[http://www.walnuts.org/walnuts101/index.php Informations about history, processing and health]
*[http://www.wvu.edu/~agexten/hortcult/fruits/blkwalnt.htm Juglone toxicity]
*[http://www.efloras.org/florataxon.aspx?flora_id=40&taxon_id=116860 Flora of Bolivia: ''Juglans'']
*[http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=116860 Flora of China: ''Juglans'']
*[http://rbg-web2.rbge.org.uk/cgi-bin/nph-readbtree.pl/feout?FAMILY_XREF=&GENUS_XREF=Juglans&SPECIES_XREF=&TAXON_NAME_XREF=&RANK= Flora Europaea: ''Juglans'']
*[http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=116860 Flora of North America: ''Juglans'']
*[http://www.efloras.org/florataxon.aspx?flora_id=5&taxon_id=116860 Flora of Pakistan: ''Juglans'']
*[http://www.efloras.org/florataxon.aspx?flora_id=201&taxon_id=116860 Trees of the Andes: ''Juglans'']
*[http://news.bbc.co.uk/2/hi/health/6036409.stm BBC article] lead to a reported 80% increase in demand at Waitrose. (ref. radio 4 news).
*[http://www.bbc.co.uk/radio4/factual/opencountry_20020330.shtml Walnut growing for timber research in the UK]
*Brinkman, K. A. (1974). Juglans L. - Walnut. In: Schopmeyer, C. S., ed. ''Seeds of woody plants in the United States''. Agriculture Handbook No. 450. Washington, DC: U.S. Department of Agriculture, Forest Service: 454-459.
*Hemery, G.E. and S.I. Popov, The walnut (Juglans regia L.) forests of Kyrgyzstan and their importance as a genetic resource. Commonwealth Forestry Review, 1998. 77(4): p. 272-276.
*Hemery, G. E. (2001). Growing walnut in mixed stands. ''Quart. J. Forestry'' 95: 31-36.
[[Category:Fagales]]
[[Category:Edible nuts and seeds]]