Walnut trees are highly valued. In the wild, squirrels and birds eat the nuts, birds such as the screech owl nest in its branches, and deer browse on the leaves. Humans cultivate the nut for consumption and use the timber from the black walnut for cabinetmaking, furniture and interior finishing.
The black walnut is found throughout the eastern U.S. into the Midwest and south into Texas. The tree emits a toxic substance called juglone that prevents other trees or plants from growing in its vicinity. Its timber is dark brown and used for cabinetmaking. The tree reaches a height of 100 feet. The bark ranges in color from a dark grayish-brown to light gray and is smooth when young, becoming grooved and cracked when older. The spear-shaped leaves are pinnate, which means individual leaflets grow in rows along a stem or axis. There are nine to 17 leaflets growing along each axis, according to "The Illustrated Encyclopedia of Trees of the World." The leaflets are dark green and shiny during the summer and turn yellow in the fall. The flowers are catkins and yellow-green, appearing separately on the same tree in the late spring and early summer. The nuts appear in the fall and are covered by a dense shell.
The Arizona walnut grows in the wild along the grasslands, canyons, and desert and mountain streams of mid to southern Arizona and in parts of southwest Texas. A small tree, the Arizona walnut ranges in height from 30 to 50 feet. The bark is light to dark brown with deep grooves and cracks. The leaves are pinnate, and each axis contains nine and 15 leaflets, according to the "Field Guide to Trees of North America." The leaflets range in color from green to greenish-yellow during the summer and turn yellow in the fall. The catkins appear before the leaves in the spring. The nuts appear in the early fall and are covered with a hairy husk.
Southern California Walnut
The southern California walnut is also called the California black walnut. It is found along the California coast, from Santa Barbara to the San Bernardino Mountains. The tree population has been decimated by urbanization and is listed as threatened, according to the U.S. Department of Agriculture Forest Service. The tree ranges in height from 20 to 49 feet. Southern California walnut trees found in stands have multiple trunks emanating from a base in the form of a "V." Trees growing alone develop single trunks. The bark is brownish-black and becomes deeply fissured as the tree ages. The leaflets are pinnate and contain nine to 17 leaflets along the axis. The leaflets are green in the summer and turn yellow or brown in the fall. The nuts appear in early fall and are covered by a thin husk that turns from green to dark brown.