The Black Walnut (Juglans nigra) is a valuable native species of eastern North America, prized for its dark, durable lumber and distinctively flavored nuts. This large deciduous tree can reach heights of 75 to 100 feet. Identifying this species requires observing a combination of features, including the trunk’s texture, the leaves’ structure, and the fruit’s unique characteristics.
Bark and Overall Structure
The mature Black Walnut has striking bark that serves as a reliable identifier throughout the year. The bark is typically dark gray to black and is deeply furrowed with sharp, narrow ridges. On older trees, these ridges often intersect, forming a recognizable diamond-shaped pattern on the trunk.
In dense forests, the tree develops a tall, straight trunk with few lower branches. Conversely, trees growing in open areas often have a shorter trunk supporting a broad, rounded crown. This overall shape and the dark, rough bark are strong indicators, even when leaves are absent in winter.
Leaf and Branch Characteristics
The foliage is a primary seasonal identifier, consisting of large, pinnately compound leaves arranged alternately on the stem. Each leaf is long, ranging from one to two feet, and is composed of 15 to 23 small, finely serrated leaflets.
A helpful diagnostic feature involves the terminal leaflet at the tip of the leaf stem. On the Black Walnut, this leaflet is often absent or significantly reduced, giving the leaf an “even-pinnate” appearance. For a definitive check, a cross-section of a twig reveals a unique light brown, chambered pith, which looks like a series of small, hollow compartments.
The Fruit and Distinctive Aroma
The tree’s fruit is its most distinctive feature, appearing as a spherical, greenish-yellow ball up to three inches in diameter. This thick, fleshy husk is smooth and does not split open while attached to the tree. The entire fruit falls to the ground in autumn, where the husk darkens and decays to reveal the corrugated, hard-shelled nut inside.
Crushing the leaves, stems, or the green husk releases a strong, pungent, spicy aroma, often described as citrus-like or similar to turpentine. This characteristic odor is a quick way to confirm the tree’s identity. The husks also contain a dark brown to black dye that easily stains skin and clothing.
Distinguishing from Look-alikes
Several trees can be mistaken for Black Walnut, most commonly the Butternut (Juglans cinerea) and various Hickory species. Butternut, also known as White Walnut, shares the pinnately compound leaves and chambered pith. However, its fruit is oblong or oval-shaped, rather than spherical, and its bark tends to be smoother and lighter gray on mature trees.
Hickory species also have compound leaves but feature fewer and larger leaflets. Unlike the Black Walnut’s smooth husk, Hickory nuts are enclosed in a woody husk that splits cleanly into four sections when ripe. The Tree-of-Heaven (Ailanthus altissima) has similar compound leaves, but its crushed foliage emits a rancid odor, and it produces clusters of winged, single-seed fruits called samaras, not spherical nuts.