The Black Walnut tree (Juglans nigra) is a prominent native hardwood species across much of eastern North America. It is recognized for its superior timber and its distinctive appearance. Understanding the visual characteristics of this species allows for accurate identification throughout the year. This guide describes the physical markers that distinguish the Black Walnut from other common forest trees.
Overall Form and Canopy
Mature Black Walnuts frequently reach heights between 70 and 100 feet, with the trunk often exceeding two to three feet in diameter in older trees. When growing in a dense forest, the tree develops a straight, clear trunk (bole) with branches beginning high off the ground as it competes for sunlight.
In open environments, the tree develops a broader, more rounded crown, with lower branches persisting closer to the ground. The overall silhouette can appear irregular or asymmetrical. As the tree ages, the lower limbs shed, leading to a high, spreading canopy that allows significant light penetration to the forest floor.
The Distinctive Bark
The bark of a mature Black Walnut offers a reliable identification feature, remaining constant through all seasons. Its color is typically dark brown or grayish-black. The surface of the trunk is deeply furrowed, creating a pattern of thick, interlacing ridges.
These pronounced ridges often form a characteristic diamond-shaped pattern resembling alligator hide. This rough texture develops over many years; bark on younger trees is noticeably smoother and lighter in color. The heavy ridging indicates that the tree has reached maturity.
Identifying Leaves and Fruit
The foliage is a significant seasonal identifier due to its size and structure. The leaves are pinnately compound, meaning multiple individual leaflets are arranged along a central stem. They are alternately positioned along the branch, and a fully developed leaf can measure between one and two feet in length.
Each compound leaf typically contains 15 to 23 leaflets. These leaflets are ovate-lanceolate, tapering to a point, and possess fine serrations (small saw-like teeth) along their edges. Before dropping in the fall, the leaves often turn a bright yellow color, adding a distinct seasonal marker.
During late summer and fall, the tree produces its signature spherical fruit, often hanging in small clusters. This fruit is encased in a thick, lime-green, fleshy husk up to two inches in diameter. When the outer husk is damaged or crushed, it releases a distinct, sharp, citrus-like fragrance. Beneath the fleshy layer is the actual nut, which is hard, dark brown, and marked by deep, irregular grooves. The presence of this round, green fruit confirms the tree’s identity during the growing season.
Twigs and Pith: Key for Winter Identification
When the tree is leafless, the structure of the twigs provides definitive identification details. The most unique feature is the pith, the spongy tissue found in the center of the twig. Unlike most trees, the Black Walnut possesses a chambered or diaphragmed pith.
This structure appears dark brown and is separated into small, hollow compartments by thin walls of tissue. To check for this feature, a twig must be carefully cut lengthwise, revealing the segmented interior. The leaf scars, left behind where the old leaf stems were attached, are large and shield-shaped, containing three distinct bundle traces. The terminal bud is small, grayish, and blunt.