|Juglans subsp. var.||Walnuts|
Walnuts (genus Juglans) are plants in the family Juglandaceae. 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. The Latin name, Juglans, derives from Jupiter glans, "Jupiter's acorn": figuratively, a nut fit for a god.
The word 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). The walnut was so called because it was introduced from Gaul and Italy. The Latin name for the walnut was nux Gallica, "Gallic nut".
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 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. 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.
|Standard Cyclopedia of Horticulture|
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.
Deciduous trees, rarely shrubs: branches with lamellate pith: lvs. alternate, without stipules, odd- pinnate, of aromatic fragrance when bruised: staminate fls. with a 2-5-lobed perianth and 6-30 stamens, in slender catkins; pistillate fls. in few- to many-fld. racemes; ovary inferior, 1-celled, with 4 calyx-lobes and included in a 3-lobed involucre: fr. a large drupe with a thick, indehiscent husk; nut 2- or 4-celled at the base, indehiscent or separating at last into 2 valves. —About 15 species in N. and S. Amer. and from S. E. Eu. to E. Asia; 44 species have been distinguished and described in a monograph by Dode (B.S.D. 1906: 67-97; 1909: 22-50, 165-215, with many illustrations).
The walnuts are usually tall broad-headed trees with large leaves, and with small greenish flowers, the staminate in pendulous slender often conspicuous catkins, the pistillate inconspicuous followed by a greenish large drupe containing an edible nut. Most of the species are hardy, and are very valuable park trees, with a massive, straight trunk, and a light and airy broad top, the best being probably J. nigra, one of the noblest trees of the American forest. J. regia, J. rupestris, and J. cathayensis are hardy as far north as Massachusetts, while J. californica is tender in the North. Though many fungi and insects prey on the walnut, none of them does very serious damage, the worst being, perhaps, the hickory-borer. The wood of the walnut, which is easily worked and susceptible of receiving a beautiful polish, is much used for cabinet making and the interior finish of houses, especially that of J. nigra and J. regia, which is heavy, strong and durable, and of dark brown color, while that of J. cinerea and J. Sieboldiana is light and soft. The husks of the nuts are sometimes used for dyeing yellow, and the bark for tanning leather. The husk of J. cinerea has some medicinal properties. The nuts of all species are edible, and are an article of commercial importance, especially those of J. regia, which are the best. This species is extensively grown in the warmer parts of Europe, in California and in the East from Pennsylvania to Georgia. The nuts of the native species are also sold on the market, but mostly gathered in the woods, though a number of improved varieties are in cultivation. J. sieboldiana and var. cordiformis, with nuts superior to those of the native species, and much valued in Japan, will probably become valuable nut trees where J. regia is too tender; also J. regia var. sinensis is hardier than the type.
The walnut grows best in moderately moist, rich soil, but J. cinerea is more moisture-loving and J. regia prefers well-drained hillsides. They are not easily transplanted when older, and therefore the nuts are often planted where the trees are to stand, but they may be safely transplanted when two or three years old, or even later when they have been transplanted in the nursery. Propagation is by seeds, which should be stratified and not allowed to become dry. A light, sandy soil is to be preferred, as the young plants produce more fibrous roots, while in stiff soil they are liable to make a long taproot. The young seedlings are transplanted when about two years old; sometimes the taproot is cut by a long knife. Varieties are often grafted on potted stock in the greenhouse in early spring or are budded in summer, either shield- or flute- budding being employed; even top-grafting of old trees is sometimes practised. For culture and further information, see United States Department of Agriculture, "Nut Culture in the United States," quoted below as U. S. N. C.; see, also, Walnut.
Index. ailantifolia, 10. alata, 12. allardiana, 10. aspleniifolia, 1. bartheriana, 1. californica, 4, 5. cathayensis, 8. cinerea, 7. coarctata, 10. corcyrensis, 1. cordiformis, 10. draconis, 8. duclouxiana, 1. elongata, 1. fertilis. 1. filicifolia, 1. fruticosa, 1. gibbosa, 11. hindsii, 5. intermedia, 11, 12. laciniata, 1. lavallci, 10. major, 2. mandshurica, 9. monophylla, 1. nigra, 6. ovoidea, 6. pendula, 1. praeparturiens, 1. pyriformis, 11. quadrangulata, 12. quercina, 5. quercifolia, 5. regia, 1. rupestria, 2, 3. sieboldiana, 10. sinensis, 1. subcordiformis, 10. torreyi, 2. vilmoreana, 11. vitmoriniana, 11.
Besides these described above, several other hybrids have been reported. Luther Burbank raised a hybrid between J. hindsii and J. nigra, named "Royal," with large nuts of excellent flavor, and one between J. Hindsii and J. regia, named "Paradox," a very vigorous grower, but a shy bearer. There are supposed hybrids between J. mandschurica X J. regia, J. cinerea XJ. nigra and J. cinerea X J. rupestris; J. longirostris, carr. (R. H. 1878, p. 53), may be a hybrid between J. regia and J. major, which often has a fr. similar in shape to the one figured.—J. australis. Griseb. Allied to J. rupestris. lfts. 13-21, large, ovate-oblong, abruptly acuminate, serrate, viscid- pubescent: nut ovoid, acute, small, slightly grooved. Argentina.— J. collapsa, Dode. Allied to J. mandschurica and probably only a variety, but nut less rugose, less sharply angled, with ovoid depressions. Probably from N. China.—J. kamadnia, Dode (J. regia var. kamaonia, DC.). Allied to J. regi. Lfta. 5-11, oblong-elliptic to oblong-lanceolate, puberulous on both sides, rufous-pubescent on the veins beneath: nut globose, rather hard-shelled. Himalayas. —J. stenocorpa, Maxim. Closely allied to J. mandschurica. Lfts. narrower, more coarsely serrate, more pubescent, the terminal 1ft. very large: fr. more oblong, less strongly ridged. Manchuria. Alfred Rehder
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).
Pests and diseases
The genus Juglans is divided into four sections.
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.
- Sect. Juglans. Leaves large (20–45 cm) with 5–9 broad leaflets, hairless, margins entire. Wood hard. Southeast Europe to central Asia.
- 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.
- 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
- 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
The best-known member of the genus is the 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 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 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 (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.
- 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
- ↑ 1.0 1.1 Online Etymology Dictionary - "Walnut"
- ↑ http://fruitandnuttrees.com/walnut-tree-j-regia-j-nigra Fruit and Nut Trees
- ↑ 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
- Standard Cyclopedia of Horticulture, by L. H. Bailey, MacMillan Co., 1963