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|name_ref=Flora - A Gardener's Encyclopedia ISBN 0881925381
|name_ref=Flora - A Gardener's Encyclopedia ISBN 0881925381
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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", ''wealh'' meaning "foreign" (''wealh'' is akin to the terms [[Wiktionary:Welsh|Welsh]] and [[Vlach]]; see [[Walha]] and [[History of the term Vlach]]).<ref name=OED>[http://www.etymonline.com/index.php?search=walnut&searchmode=none Online Etymology Dictionary - "Walnut"]</ref> The walnut was so called because it was introduced from [[Gaul]] and [[Italy]]. The [[Latin]] name for the walnut was ''nux Gallica'', "[[Gaul|Gallic]] nut".<ref name=OED/>
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.
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.
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>
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Juglans (ancient Latin name from Jovis glans, nut of Jupiter). Juglandaceae. Walnut. Butternut. Plate LX. Woody plants grown for their handsome foliage and some species for their edible nuts.
Juglans (ancient Latin name from Jovis glans, nut of Jupiter). Juglandaceae. Walnut. Butternut. Plate LX. Woody plants grown for their handsome foliage and some species for their edible nuts.
==Cultivation==
==Cultivation==
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).
===Propagation===
===Propagation===
==Varieties==
==Varieties==
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>
Sections and species:
*'''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]].
**''[[Juglans ailantifolia|J. ailantifolia]]'' Carr. (''J. cordiformis'' Maxim., ''J. sieboldiana'' Maxim.) — Japanese Walnut
***[[heartnut|''J. ailantifolia'' var. ''cordiformis'']] — Heartnut
**''[[Juglans mandshurica|J. mandshurica]]'' Maxim. (''J. cathayensis'' Dode, ''J. formosana'' Hayata, ''J. hopeiensis'' Dode, ''J. stenocarpa'' Maxim.) — Manchurian Walnut or Chinese Walnut.
*'''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'''''. (The '''black walnuts''') 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. brasiliensis'' Dode) — Argentine Walnut, Brazilian Walnut
**''[[Juglans boliviana|J. boliviana]]'' (C. DC.) Dode — Bolivian walnut, Peruvian 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 León 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|J. microcarpa]]'' Berlandier (''J. rupestris'' Engelm.) — Texas Walnut or Little Black Walnut
***''J. microcarpa'' var. ''microcarpa''
***''J. microcarpa'' var. ''stewartii'' (Johnston) Manning
**''[[Juglans mollis|J. mollis]]'' Engelm. — [[Mexican Walnut]]
**''[[Juglans neotropica|J. neotropica]]'' Diels (''J. honorei'' Dode) — Andean Walnut, Cedro Negro , Cedro Nogal , Nogal , Nogal Bogotano
**''[[Juglans nigra|J. nigra]]'' L. — Eastern Black Walnut
**''[[Juglans olanchana|J. olanchana]]'' Standl. & L.O.Williams — Cedro Negro, Nogal , Walnut
***''J. olanchana'' var. ''olanchana''
***''J. olanchana'' var. ''standleyi''
**''[[Juglans boliviana|J. peruviana]]'' Dode — Peruvian Walnut
**''[[Juglans soratensis|J. soratensis]]'' Manning
**''[[Juglans steyermarkii|J. steyermarkii]]'' Manning — [[Guatemalan Walnut]]
**''[[Juglans venezuelensis|J. venezuelensis]]'' Manning — Venezuela 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]].
**''[[Juglans cinerea|J. cinerea]]'' L. — Butternut
[[File: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]]. Walnuts are a traditional feature of [[Iranian cuisine]]; the nation has extensive orchards which are an important feature of regional economies. 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."
The [[Black Walnut|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, 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 [[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 eastern 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.
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, very slender ridges, and the kernel is especially high in fat.
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''
==Gallery==
==Gallery==