The walnut tree genus, known botanically as juglans, contains at least 17 species and hybrid cultivars of walnut trees. Walnut trees are a fine hardwood trees related to the hickory genus and are grown for their nuts and timber wood. All species fall into one of three types of walnut tree: those grown for their fruit or nuts, those grown for timber, and those grown for both their fruit and timber. Waste from the nut and timber harvest industries are also commercially refined and sold for secondary product purposes including walnut oil and indelible dyes made with the skin of the black walnut. Walnut trees are also widely grown as specimen or ornamental trees due to their large patrician profile, elegant trunks and attractive broad canopy.
Common Walnut Trees
Walnut trees that are not hybrid or black walnut species are grouped together as common walnut and this is the largest species group in the genus. Common walnut trees are grown for their fruit, their timber or as ornamentals. Common walnut species include the Japanese walnut; Bolivian walnut; Southern California walnut; butternut walnut; Northern California walnut, West Indian walnut, Arizona walnut; Manchurian walnut; little walnut; Stewart's little walnut; Andean walnut and the English walnut.
Black Walnut Trees
Black walnut trees are grown for their fruit as well as their timber wood and are distinguished by the dark, nearly indelible ink secreted from their outer skins when the peel is breached. The main species of black walnut is Juglans nigra.
Hybrid Walnut Trees
Hybrid walnut trees are mainly grown for their timber harvest and have been bred for speedier growth and dense wood with a tight grain. Hybrid walnut tree species include juglans x bixbyi Rehder, juglans x intermedia Carrière, and juglans x quadrangulata Carrière Rehder.