The walnut tree, a member of the genus Juglans, is a large, deciduous species prized for its valuable wood and edible nuts. Recognizing a walnut tree requires observing several distinct physical features, including the bark texture, leaf structure, and the unique appearance of its fruit. Identification is possible even when the tree is not bearing nuts, by focusing on the overall form and specific botanical details.
Overall Tree Structure and Bark
Mature walnut trees often develop an imposing stature, reaching heights between 70 and 100 feet with a correspondingly wide, rounded canopy. When growing in a forest environment, the tree tends to develop a long, straight trunk with few lower branches as it reaches for sunlight. In open areas, however, the trunk may be shorter, dividing into large, spreading branches that create a broad silhouette.
The bark provides one of the most reliable identification markers, especially in winter when leaves are absent. Young walnut trees initially have smoother, lighter gray or brownish bark that can appear flaky. As the tree ages, the bark develops deep, coarse furrows and thick, sharp ridges that run vertically up the trunk. This pattern often creates a rough, blocky appearance, sometimes described as resembling an alligator hide or forming a distinct diamond shape on older specimens.
Identifying Leaves and Branch Characteristics
Walnut leaves are compound, meaning they are composed of multiple smaller leaflets attached to a central stem. They are arranged alternately along the stout twigs, and a single compound leaf can measure up to two feet long. The number of leaflets varies by species, typically ranging from 5 to 23 on a single leaf.
A distinctive feature is that the leaflets are often asymmetrical at their base and may have finely serrated edges, though this varies by species. Crushing the leaves or scraping the bark often releases a characteristic, pungent odor, sometimes likened to a spicy citrus or lemon-lime scent. The internal structure of the twig offers a unique clue: if cut lengthwise, the central pith is divided into small, hollow sections separated by fibrous walls, a feature known as chambered pith.
Appearance of the Walnut Fruit and Nut
The fruit of the walnut tree first appears as a conspicuous, roughly spherical green ball hanging from the branches. This green sphere is the husk, which is thick and firm, measuring about two inches or more in diameter. The fruit typically grows singly or in small clusters of two or three.
As the fruit matures and falls in the autumn, the green husk darkens to a brown or black color and can be quite messy. The husk contains a watery, dark juice that readily stains skin and clothing a tenacious brown or black color. Once the husk is removed, the hard, woody nut shell is revealed, which is brown or dark brown and heavily grooved or corrugated.
Distinguishing Black Walnut from English Walnut
Visual differences exist between the two most commonly encountered types, the Black Walnut (Juglans nigra) and the English Walnut (Juglans regia). The bark of the native Black Walnut is typically dark gray to black and is more deeply and roughly furrowed, often with a diamond-patterned texture. The English Walnut, the species most commonly grown for commercial nuts, tends to have lighter, grayer bark that is smoother when young, developing deep fissures but often lacking the pronounced blocky ridges of its Black Walnut cousin.
Leaf Differences
Black Walnut leaves are significantly larger and have a higher number of leaflets, usually ranging from 15 to 23, with the terminal leaflet often missing or very small. English Walnut leaves have fewer leaflets, typically between five and nine, and the edges of the individual leaflets are smooth rather than serrated.
Fruit and Nut Differences
The fruit husk of the Black Walnut is generally rounder, thicker, and non-splitting, enclosing a nut with a notably harder shell and deeper ridges. Conversely, the English Walnut husk is sometimes thinner and the resulting shell is smoother and easier to crack.