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Juglans nigra, the eastern American black walnut, is a species of deciduous tree in the walnut family, Juglandaceae, native to central and eastern North America, growing mostly in .
Black walnut is susceptible to thousand cankers disease, which provoked a decline of walnut trees in some regions. Black walnut is allelopathic, releasing chemicals from its roots and other tissues that may harm other organisms and give the tree a competitive advantage, but there is no scientific consensus that this is a primary competitive factor.
Black walnut is an important tree commercially, as the wood is a deep brown color and easily worked. Walnut (nuts) are cultivated for their distinctive and desirable taste. Walnut trees are grown for lumber and food, and processors have found additional markets for even the tough outer hulls by finely grinding them for use in products such as abrasive cleansers. Many have been developed for improved quality wood or nuts. In 2017, the United States Department of Agriculture valued U.S. walnut timber at $530 billion. A significant amount is grown in Missouri.
The pith of the twigs is chambered and light brown. The are pale silky and covered in downy hairs. The terminal buds are ovate, and long, and slightly longer than broad, the lateral buds are smaller and superposed.
The leaves are pinnately compound and alternately arranged on the stem. They are long, typically even-pinnate but there is heavy variation among leaves. The stems have 15–23 leaflets, when terminal leaf is included, with the largest leaflets located in the center, long and broad. (1990). 9780875633442, Stipes Publishing Company. ISBN 9780875633442 The leaflets have a rounded base and a long pointed (acuminate) tip as well as having a serrated edge. (2007). 9780812240030, University of Pennsylvania press. ISBN 9780812240030 The leaves are overall dark green in color and are typically hairy on the underside.
The leaf scar has three prominent bundle scars and has a notch on the side that points toward the tip of the branch (distal side).
Black walnut is monoecious. The male (staminate) flowers are in drooping catkins long. These are borne from axillary buds on the previous year's growth. The female (pistillate) flowers are terminal, in clusters of two to five on the current year's growth. During the summer/autumn, a spherical fruit (nut) ripens. It comprises a brownish-green, semifleshy husk and a brown, corrugated nut. The whole fruit, including the husk, falls in October; the seed is relatively small and very hard.
Most parts of the tree including leaves, stems, and fruit have a very characteristic pungent or spicy odor. This odor is lacking in the nut itself.
Black walnut's native range extends across much of the eastern US. It is absent from the coastal plain south of North Carolina as well as the Mississippi Valley, and does not occur in the northern tier of the eastern US, where the frost-free season is too short for the nuts to develop. Its western range extends all the way to the eastern Great Plains, beyond which climate conditions become too dry for it.
Black walnut is one of the most abundant trees in the eastern US, particularly the Northeast, and its numbers are increasing due to epidemics that have affected other tree species, including emerald ash borer, chestnut blight, butternut canker, wooly hemlock adelgid, dogwood anthracnose, Dutch elm disease, and spongy moth infestations. Widespread clear-cutting of oaks due to spongy moth damage in the 1970s–1980s particularly aided in the tree's spread. The aggressive competitive strategy of black walnut such as its fast growth, alleopathic chemicals, and rodent-dispersed seeds, have also contributed.
The nuts are food for many rodents and make up to 10% of the diet of eastern fox squirrels. The nuts are also eaten by species of birds. The leaves are browsed by white tailed deer, although they are not a preferred food.
Where the range of the eastern black walnut overlaps that of the Texas black walnut ( J. microcarpa), the two species sometimes interbreed, producing populations with characteristics intermediate between the two species. J. nigra and J. cinerea often grow in the same range as well but they do not hybridize naturally.
The tree's roots often form relationships with fungi in the genus Glomus. Some endomycorrhizal relations improve the plant's growth.
Species often associated with J. nigra include yellow-poplar ( Liriodendron tulipifera), white ash ( Fraxinus americana), black cherry ( Prunus serotina), basswood ( Tilia americana), American beech ( Fagus grandifolia), sugar maple ( Acer saccharum), ( Quercus spp.), and hickory ( Carya spp.). Near the western edge of its range, black walnut may be confined to floodplains, where it grows either with American elm ( Ulmus americana), common hackberry ( Celtis occidentalis), green ash ( Fraxinus pennsylvanica), and boxelder ( Acer negundo), or with basswood and red oak ( Quercus rubra) on lower slopes and other favorable sites.
The walnut weevil ( Conotrachelus retentus) grows to long as an adult. The adult sucks plant juices through a snout. The eggs are laid in fruits in the spring and summer. Many nuts are lost due to damage from the larvae, which burrow through the nut shell.
Black walnut is affected by European canker ( Neonectria galligena). The infection spreads slowly but infected trees eventually die.
The walnut caterpillar ( Datana integerrima) and fall webworm ( Hyphantria cunea) are two of the most serious pests, they commonly eat the foliage in midsummer and continue into autumn.
Codling moth ( Cydia pomonella) larvae eat walnut kernels, as well as apple and pear seeds.
Important leaf sucking insects include species of and plant lice including ( Monellia spp. and Monelliopsis spp.), which suck the juices from leaves and often deposit a sticky substance called "honey-dew" on the leaf surface that may turn black and prevent photosynthesis; and the walnut lace bug ( Corythucha juglandis), which causes damage when the adults and nymphs suck the sap from the lower surfaces of walnut leaflets.
A disease complex known as thousand cankers disease has been threatening black walnut in several western states. This disease has recently been discovered in Tennessee, and could potentially have devastating effects on the species in the eastern United States. Vectored by the walnut twig beetle ( Pityophthorus juglandis), a fungus, Geosmithia morbida, spreads into the wood around the galleries carved by the small beetles. The fungus causes cankers that inhibit the movement of nutrients in black walnut, leading to crown and branch dieback, and ultimately death.
Like other walnuts, the roots, inner bark, nut husks, and leaves contain a nontoxic chemical called hydrojuglone; when exposed to air or soil compounds it is oxidized into juglone that is biologically active and acts as a respiratory inhibitor to some plants. Juglone is poorly soluble in water and does not move far in the soil and will stay most concentrated in the soil directly beneath the tree. Even after a tree is removed the soil where the roots once were will still contain juglone for several years after the tree is removed as more juglone will be released as the roots decay. Well drained and aerated soils will host a healthy community of soil microbes and these microbes will help to break down the juglone.
Symptoms of juglone poisoning include foliar yellowing and wilting. A number of plants are particularly sensitive. Apples, tomatoes, pines, and birch are poisoned by juglone, and as a precaution, should not be planted in proximity to a black walnut.
Black walnut is more resistant to frost than Juglans regia (the English or Persian walnut), but thrives best in the warmer regions of fertile, lowland soils with high water tables, although it will also grow in drier soils, but much more slowly. Some specimens have been found to survive frosts down to . Some soils preferred by black walnut include alfisol and entisol soil types. Black walnut grows best on sandy loam, loam, or silt loam type soils but will also grow well on silty clay loam soils. It prefers these soils because they hold large quantities of water, which the tree draws from during rainless periods.
Grafted, nut-producing trees are available from several nurseries operating in the U.S. Selections worth considering include Thomas, Neel #1, Thomas Myers, Pounds #2, Stoker, Surprise, Emma K, Sparrow, S127, and McGinnis. Several older varieties, such as Kwik Krop, are still in cultivation; while they make decent nuts, they would not be recommended for commercial planting.
Pollination requirements should be considered when planting black walnuts. As is typical of many species in Juglandaceae, J. nigra trees tend to be monoecious, i.e.. produce pollen first and then pistillate flowers or else produce pistillate flowers and then pollen. An early pollen-producer should be grouped with other varieties that produce pistillate flowers so all varieties benefit from overlap. Cranz, Thomas, and Neel #1 make a good pollination trio. A similar group for more northern climates would be Sparrow, S127, and Mintle.
Sometimes black walnut is planted as part of reclaiming mines. When growing young trees weed control is critical for healthy establishment of the trees, without weed control the young trees are harmed significantly in their growth rate.
The shell itself is thicker than that of the English walnut, and there are additional, thick internal walls tightly surrounding the nutmeat. Walnuts are too tough and too large to be opened with a standard nutcracker, but simply cracking the shell open with a rock results in smashed and shattered nutmeats mixed with shell, unless done with some care and skill—and it is still nearly impossible to extract an intact half this way. As a result, a number of home walnut-cracking devices have been produced, involving vices, cams, or levers.
While the flavor of the Juglans nigra kernel is prized, the difficulty in preparing it may account for the wider popularity and availability of the English walnut.
Tapped in spring, the tree yields a sweet sap that can be drunk or concentrated into syrup or sugar that is not unlike the sap of sugar maple.
Analysis of black walnut fat content showed the most prevalent are linoleic acid (33.8%), followed by oleic acid (15.3%), alpha-linolenic acid (2.7%), palmitic acid (1.9%), and stearic acid (1.5%).
Walnut wood has historically been used for , furniture, flooring, paddles, coffins, and a variety of other wood products. Black walnut has a density of 660 kg per cubic meter (41.2 lb/cubic foot), which makes it less dense than oak.
The tallest black walnut in Europe is located in the Woluwe Park in the city of Sint-Pieters-Woluwe, Brussels, Belgium. It has a circumference of , height of exactly (measured by laser), and was planted around 1850 (± 10 years).
The largest black walnut in Europe is located in the Castle Park in the city of Sereď, Slovakia. It has a circumference of , height of and estimated age of 300 years.
Dye
Black walnut contain juglone (5-hydroxy-1,4-naphthoquinone), plumbagin (yellow quinone pigments), and tannin. These compounds cause walnuts to stain cars, sidewalks, porches, and patios, in addition to the hands of anyone attempting to shell them. The brownish-black dye was used by early American settlers to dye hair. According to Eastern Trees in the Petersen Guide series, black walnuts make a yellowish-brown dye, not brownish-black. The apparent confusion is easily explained by the fact that the liquid (dye) obtained from the inner husk becomes increasingly darker over time, as the outer skin darkens from light green to black. Extracts of the outer, soft part of the drupe are still used as a natural dye for handicrafts. The tannins present in walnuts act as a mordant, aiding in the dyeing process, and are usable as a dark ink or wood stain.
Shells
Walnut shells are often used as an abrasive in sand blasting or other circumstances where a medium hardness grit is required. The hard black walnut shell is also used commercially in abrasive cleaning, a filtering agent in scrubbers in smoke stacks, cleaning jet engines, cosmetics, and oil well drilling and water filtration. Additionally, the husks are ground into an ingredient in exfoliating cosmetics.
Wood
Black walnut is highly prized for its dark-colored, straight grained, true heartwood. It is heavy, strong, shock resistant and yet can be easily split and worked. Along with cedars (Thuja), chestnut ( Castanea spp.), and black locust ( Robinia pseudoacacia) black walnut is one of the most durable hardwoods in the US. The wood can be kiln dried and holds its shape well after seasoning, which makes this wood even more attractive for wood working.
Largest trees
The U.S. national champion black walnut is on a residential property on Sauvie Island, Oregon. It is diameter at breast height and tall, with a crown spread of .
See also
Further reading
External links
Categories: Nigra, Edible Nuts And Seeds, Flora Of The Appalachian Mountains, Symbols Of Missouri, Trees Of Humid Continental Climate, Plants Described In 1753, Botanical Taxa Named By Carl Linnaeus, Plant Dyes, Garden Plants Of North America, Ornamental Trees, Flora Of Texas, Trees Of Northern America
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