What is Black Walnut? Black walnut (Juglans nigra), also known as American walnut, is a species of tree native to eastern North America, the Himalayas, Kyrgyzstan and Central Asia. The trees can reach a height of up to 100 feet and have roots as deep as 10 feet. How will Black Walnut help me? Black Walnut is a good source of protein, nutrients such as iodine, chromium, potassium, the trace mineral manganese and antioxidant Vitamins A and C. Herbalists classify black walnut as an astringent because it is rich in tannins, which have toning properties. Black walnut also contains bitter compounds. Through the ages, it has proven to be an effective yet gentle support to the intestinal system. The ancient Greeks used the hulls of black walnut to support the intestinal system and the skin. Is Black Walnut suitable for everyone? Black Walnut is not suitable for use during pregnancy, or by those trying to conceive. Or for those with nut allergies.