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|image_caption=Shoot and nut of ''Juglans regia''
|image_caption=Shoot and nut of ''Juglans regia''
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'''Walnuts''' (genus ''Juglans'') are [[plant]]s in the family [[Juglandaceae]]. They are [[deciduous]] [[tree]]s, 10–40 [[meter (unit)|meter]]s tall (about 30–130 [[foot (length)|ft]]), with [[pinnate]] leaves 200–900 millimetres long (7–35 [[inch|in]]), with 5–25 leaflets; the shoots have chambered [[pith]], a character shared with the [[wingnut (plant)|wingnuts]] (''Pterocarya'') but not the [[hickory|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 ''[[Jupiter_(mythology)|Jupiter]] [[glans]]'', "Jupiter's acorn": figuratively, a nut fit for a god.
The word ''walnut'' derives from [[Old English language|Old English]] ''wealhhnutu'', literally "foreign nut".
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Walnut (formerly sometimes written wallnut, but the name has no connection with wall, being rather of Anglo-Saxon derivation signifying "foreign nut," as the product came from the continent). A name applied to Juglans regia and its fruit, to us known mostly as English walnut because the supply yearly reached America through England; also, by extension, to other species of the genus Juglans. The name is sometimes, but provincially, given to hickory-nuts.
Walnut (formerly sometimes written wallnut, but the name has no connection with wall, being rather of Anglo-Saxon derivation signifying "foreign nut," as the product came from the continent). A name applied to Juglans regia and its fruit, to us known mostly as English walnut because the supply yearly reached America through England; also, by extension, to other species of the genus Juglans. The name is sometimes, but provincially, given to hickory-nuts.
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[[File:Noyer.JPG|thumb|Walnut tree (Juglans regia)]]
==Cultivation==
'''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:2005walnut.PNG|thumb|left|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 fixation|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 [[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 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.
==Species and classification==
===Flowers===
The leaves and blossoms of the walnut tree normally appear in spring. The male cylindrical catkins of the Walnut tree 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.<ref>http://fruitandnuttrees.com/walnut-tree-j-regia-j-nigra Fruit and Nut Trees</ref>.
[[Image:Juglans ailantifolia.jpg|right|240px|thumb|Japanese Walnut foliage and nuts]]
====Nuts and Kernels====
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.
[[Image:Walnut03.jpg|thumb|250px|left|Inside of a common walnut nut with green outer layer visible in the top left corner]]
The nut kernels of all the species are edible, but the walnuts most commonly available in shops are from the Persian walnut, the only species which has a large nut and thin shell; black walnut species are more difficult to crack and remove from the shell. One horticultural form selected for thin nut shells and hardiness in temperate zones is sometimes known as the 'Carpathian' walnut.
Of the more than 30 varieties of ''J. regia'' grown there, Chandler and Hartley account for over half of total production.[http://www.walnuts.org/walnuts101/history_cultivation_processing.php]
===Propagation===
===Pests and diseases===
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 [[rootstock]]s 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<ref>http://www.padil.gov.au/viewPestDiagnosticImages.aspx?id=601</ref>.
==Cultivations==
==Varieties==
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.
[[Image:Walnuts02.jpg|thumb|250px|right|Common walnuts]]
The genus ''Juglans'' is divided into four sections<ref>Aradhya, M. K., D. Potter, F. Gao, C. J. Simon: "Molecular phylogeny of ''Juglans'' (Juglandaceae): a biogeographic perspective",''Tree Genetics & Genomes''(2007)'''3''':363-378</ref>:
*'''Sect. ''Juglans'''''. Leaves large (20–45 cm) with 5–9 broad leaflets, hairless, margins entire. Wood hard. Southeast [[Europe]] to central [[Asia]].
**''[[Juglans regia|J. regia]]'' L. (''J. duclouxiana'' Dode, ''J. fallax'' Dode, ''J. orientis'' Dode) — common walnut, Persian, English, or Carpathian walnut
**''[[Juglans sigillata|J. 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|J. australis]]'' Griseb. (''J. boliviana'' Dode) — Argentine Walnut
**''[[Juglans boliviana|J. boliviana]]'' (C. DC.) Dode — Bolivian walnut, Peruvian walnut
**''[[Juglans brasiliensis|J. brasiliensis]]'' Dode — Brazilian Walnut
**''[[Juglans californica|J. californica]]'' S.Wats. — California Black Walnut
**''[[Juglans hindsii|J. hindsii]]'' (Jepson) R.E.Smith — Hinds' Black Walnut
**''[[Juglans hirsuta|J. hirsuta]]'' Manning — Nuevo Leon Walnut
**''[[Juglans jamaicensis|J. jamaicensis]]'' C.DC. (''J. insularis'' Griseb.) — West Indies Walnut
**''[[Juglans major|J. major]]'' (Torrey) Heller (''J. arizonica'' Dode, ''J. elaeopyron'' Dode, ''J. torreyi'' Dode) — Arizona Black Walnut
***''J. major'' var. ''glabrata'' Manning
**''Juglans 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. — [[Black Walnut|Eastern Black Walnut]]
**''[[Juglans olanchana|J. olanchana]]'' Standl. & L.O.Williams — Cedro Negro, Nogal , Walnut
**''[[Juglans boliviana|J. peruviana]]'' Dode — Peruvian Walnut
**''J. soratensis'' Manning
**''J. steyermarkii'' Manning — [[Guatemalan Walnut]]
**''[[Juglans venezuelensis|J. venezuelensis]]'' Manning — Venezuela Walnut
*'''Sect. ''Cardiocaryon'''''. Leaves very large (40–90 cm) with 11–19 broad leaflets, softly downy, margins serrated. Wood soft. Fruits borne in racemes of up to 20. Nuts have thick shells. Northeast [[Asia]].
**''J. ailantifolia'' Carr. (''J. cordiformis'' Maxim., ''J. sieboldiana'' Maxim.) — [[Japanese Walnut]]
***''J. ailantifolia'' var. cordiformis — [[Japanese Walnut|Heartnut]]
**''[[Juglans mandshurica|J. mandshurica]]'' Maxim. (''J. cathayensis'' Dode, ''J. formosana'' Hayata, ''J. hopeiensis'' Dode, ''J. stenocarpa'' Maxim.) — Manchurian Walnut or Chinese Walnut.
*'''Sect. ''Trachycaryon'''''. Leaves very large (40–90 cm) with 11–19 broad leaflets, softly downy, margins serrated. Wood soft. Fruits borne in clusters of 2-3. Nuts have a thick, rough shell bearing distinct, sharp ridges. Eastern [[North America]].
**''J. cinerea'' L. — [[Butternut (tree)|Butternut]]
[[Image:Juglans ailantifolia.jpg|right|240px|thumb|Japanese Walnut foliage and nuts]]
The best-known member of the genus is the [[Juglans regia|Persian walnut]] (''J. regia'', literally "royal walnut"), native from the [[Balkans]] in southeast [[Europe]], southwest & central [[Asia]] to the [[Himalaya]] and southwest [[China]]. This species is widely cultivated for its delicious [[nut (fruit)|nuts]]. According to the UN Food and Agriculture Organization (FAO), Shahmirzad orchard in Iran is the largest in the world (700-750 ha). In [[Kyrgyzstan]] alone there are 230,700 ha of walnut-fruit forest, where ''J. regia'' is the dominant overstory tree (Hemery and Popov 1998). In non-European English-speaking nations, the nut of the ''J. regia'' is often called the "English walnut"; in Great Britain, the "common walnut." Tuiserkan is the second city in Iran that is famous for the best quality of its walnut.{{Citation needed|date=October 2009}}
The [[Black Walnut]] (''J. 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 wood is particularly valuable.
The [[Butternut (tree)|Butternut]] (''J. 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, the fruits are oval, the shell has very tall ridges, and the kernel is especially high in fat.
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
The [[Juglans hindsii|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 that are characteristic of the black walnut (''J. nigra'').
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.
;Wood
;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''
==Gallery==
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==References==
<references/>
*[[Standard Cyclopedia of Horticulture]], by L. H. Bailey, MacMillan Co., 1963
<!--- xxxxx *Flora: The Gardener's Bible, by Sean Hogan. Global Book Publishing, 2003. ISBN 0881925381 -->
<!--- xxxxx *American Horticultural Society: A-Z Encyclopedia of Garden Plants, by Christopher Brickell, Judith D. Zuk. 1996. ISBN 0789419432 -->
<!--- xxxxx *Sunset National Garden Book. Sunset Books, Inc., 1997. ISBN 0376038608 -->
==References==
==External links==
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