BLACK WALNUT: CHARACTERISTICS, HABITAT, DISTRIBUTION, PROPERTIES - BIOLOGY - 2025

The black walnut (Juglans nigra) is an economically important tree belonging to the Juglandaceae family. It is also commonly known as eastern black walnut and hickory. This arboreal species reaches about 35 m high, has compound leaves, male flowers in catkins and female flowers in terminal spikes. The fruits contain a hard-walled nut.

It is a monoecious heterodicgam tree (the functions of the male and female flower structures are temporally separated). It is distributed mainly in North America, although it can also be found in some European countries.

The black walnut is about 35 m tall. Source: I, Jean-Pol GRANDMONT

Black walnut is one of the rarest and most coveted hardwoods in America. The nuts produced by this tree have a very particular and distinctive flavor, which is why they are in high demand in the pastry, baked goods and ice cream industries; this if, they can be harvested before the squirrels do.

characteristics

Appearance

It is a tree about 35 m tall, with scaly bark and brown or gray in color. It has branches covered with trichomes.

Leaves

Black walnut leaves are 30 to 60 cm long, have between 15 and 25 ovate-lanceolate leaflets each 7.5 to 12.5 cm long, are tapered and have serrated edges.

Regarding pubescence, the upper surface is devoid of trichomes, and the underside is pubescent especially on the central nerve. The leaves are yellowish-green.

Black walnut tree. Source: pixabay.com

flowers

Walnut has yellowish-green male flowers arranged in slender catkins that grow on axillary shoots. The female flowers are grouped in short terminal spikes and may appear several times on the shoots during the year. Trees reach reproductive maturity between 20 and 30 years.

Pollen dispersal is through the wind. Pollination normally occurs thanks to pollen from neighboring trees.

Fruit

The fruits of Juglans nigra can be solitary or formed in pairs, they measure 3 to 5 cm in diameter, are globose in shape, yellowish-green in color, form grooves when ripe, and harbor a hard-walled nut.

The dispersal of the fruits and seeds occurs thanks to rodents, especially squirrels, which are the main animals that feed on nuts. On the other hand, fruits with viable seeds can float on water, so they can also disperse long distances through hydrochoria.

Fruits of Juglans nigra. Source: pixabay.com

Taxonomy

-Kingdom: Plantae

-Filo: Tracheophyta

-Class: Magnoliopsida

-Order: Fagales

-Family: Juglandaceae

-Gender: Juglans

-Species: Juglans nigra L.

Some synonyms for black walnut are: Juglans pitteursii and Wallia nigra.

Habitat and distribution

The black walnut is a widely distributed species in deciduous forests of eastern North America. It grows in favorable places like Canada, Ontario, Kansas, New Jersey, and Florida. This tree can also be present in Austria, Denmark, Germany, Italy, Romania, Croatia, Greece, Slovenia, Ukraine and some more.

The black walnut is a pioneer species, intolerant to shade, and in natural conditions its longevity is around 250 years. It is often found in sites close to water sources, but with deep, well-drained soils with high fertility or organic matter.

The type of soils it adapts to are Alfisols and Entisols, derived from limestone. The black walnut grows best in sandy loam or silty loam soils since during the dry period they keep water available for the tree.

Generally, it is associated with species such as white oak, black oak, northern red oak, yellow poplar, white ash, black cherry, sugar maple, Quercus species, among others.

On the contrary, the toxic effect that black walnut has on other plants has been recognized. In this sense, Juglans nigra inhibits the growth of species such as birch, red pine, white pine, Scots pine, apple and tomato.

Walnut of black walnut. Source: Photo by and (c) 2007 Derek Ramsey (Ram-Man). Location credit to the Chanticleer Garden.

Properties

Different structures of the black walnut produce beneficial effects on human health. Parts such as the bark and leaves are used as anti-inflammatory, astringent, detergent, laxative, expectorant, and vermifuge.

It is a special plant to treat skin diseases such as herpes or eczema. The bark of this tree is also used to treat diarrhea and to stop milk production. A very concentrated infusion can work as an emetic.

The bark is chewed to reduce toothache, and is also used as a poultice to relieve headaches and colic. The extract from the rind of the fruit is applied to the skin to treat diseases caused by parasitic fungi, and for this purpose the powdered leaves are also applied to the affected area.

On the other hand, the grains are burned and added to red wine to be ingested and thus prevent hair loss.

With the leaves you can prepare a tea that works as an astringent, also to control hypertension, as well as to perform washes.

Also, the oil from the seeds is used externally to treat gangrene, leprosy or wounds on the skin. The sap produced by this tree is used to treat inflammation.

Black walnut structures. Source: USDA-NRCS PLANTS Database / Britton, NL, and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. Vol. 2: 487.

Other uses

The seed, whether raw or cooked, has a sweet and delicious flavor, it is used as a nut in desserts, cakes, sweets, etc.

Immature fruits are good for pickles. Walnuts, shells, and bark can serve as natural dyes. The seeds are also processed to obtain an edible oil.

Also, walnuts are used as a seasoning for bread, pumpkins, or other foods. The sap of the black walnut is very sweet and is used as a drink or to prepare syrup.

On the other hand, the shells can be processed into very good quality charcoal, which is then used as a filter. The woody shells of the fruits are used to make garments.

Extracts from black walnut and leaves are used as repellants for insects such as flies, bed bugs and fleas. In addition, the leaves have allelopathic properties, since through the rain, these substances are carried to the ground and inhibit the growth of plants under the tree.

Its wood is very ornamental, durable, strong and heavy. It is easy to work with, it does not warp and it polishes very well. This wood is one of the most sought after in North America, in fact, there are areas where the exploitation of this tree for this purpose is allowed. It is used to make cabinets, interior finishes, furniture, shipbuilding, veneers, among others.

References

1. Victory, ER, Glaubitz, J., Rhodes, O., Woeste, K. 2006. Genetic homogeneity in Juglans nigra (Juglandaceae) at nuclear microsatellites. American Journal of Botany 93 (1): 118-126.
2. Plants for a future. 2019. Juglans nigra - L. Taken from: pfaf.org
3. Williams, RD 1990. Black Walnut Juglans nigra L. In: Silvics of North America. Agriculture Handbook. Washington. Pages 391-398. Taken from: books.google.es
4. Catalog of Life: Annual Checklist 2019. Species details: Juglans nigra L. Taken from: catalogueoflife.org
5. Sánchez de Lorenzo-Cáceres, JM 2019. Juglans nigra L. Taken from: arbolesornamentales.es