Black walnut (Juglans nigra) is native to Ontario, with its natural range extending to the central and eastern United States. It is also widely planted in Europe. The species is early successional, hence light-demanding and competition-intolerant. It grows best interspersed with other tree species in rich and moist, but well-drained soils along rivers. The wood of black walnut has an appealing dark brown color and straight-grained surface. It is prized for being strong, shock resistant, and highly resistant to decay. It is widely used for sliced veneer and for solid furniture. While it has always been the most expensive wood in North America, it is also one of the most expensive furniture lumbers globally.
Indigenous peoples in North America traditionally used the oil-rich black walnut fruit as a food source. The fruit has also been used in traditional medicine to treat diarrhea, nausea/vomiting, and intestinal cramps. Even today, humans appreciate black walnut kernels as a nutritious and health-promoting food. It is high in mono-unsaturated fatty acids and antioxidants, such as polyphenolic compounds. Many of these polyphenols act as anti-inflammatory, antioxidant, antibacterial, and anti-cancerous agents, promoting black walnut’s ‘superfood’ reputation. In addition to the nut kernels, the seed husks, leaves, bark and roots of black walnut are biochemical powerhouses, producing a cocktail of secondary compounds. Juglone, a phenolic substance, is the most bioactive compound in this cocktail. Juglone acts as a toxic (allelopathic) substance, inhibiting the growth of nearby competing plant species. Crop plants such as tomatoes or apples, as well as birches, and several pine species are susceptible to juglone toxicity. Competitive seed germination and plant growth are prevented up to 18 m away from a black walnut tree. With the high economical value of its much sought-after wood, health-promoting nuts, unique biochemical profile, and role as an ornamental tree for parks and avenues, black walnut is commonly regarded as ‘the most respected of North America’s hardwoods.’
Original text written by Mira Ola, rewritten by Ayuni Ratnayake and Ivana Stehlik
Ho K.-V., Roy A., Foote S., Vo P. H., Lall N. and Lin C.-H. 2020. Profiling anticancer and antioxidant activities of phenolic compounds present in black walnuts (Juglans nigra) using a high-throughput screening approach. Molecules 25: 4516.
Nicolescu V.-N., Redei K., Vor T., Bastien J.-C., Brus R., Bencat T., Dodan M., Cvjetkovic B., Andrasev S., La Porta N., Lavnyy V., Petkova K., Peric S., Bartlett D., Hernea C., Pastor M., Mataruga M., Podrazsky V., Sfecla V. and Stefancik I. 2020. A review of black walnut (Juglans nigra L.) ecology and management in Europe. Trees 34: 1087-1112.
Photo credit: Laval University, CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0), via Wikimedia Commons