The hickory genus, Carya, encompasses approximately 19 species, with 12 species native to North America, primarily across the eastern half of the continent. These deciduous trees are common components of hardwood forests, often coexisting with oaks and maples. Identifying a hickory tree requires a close examination of several distinct features, as individual species within the genus can vary widely in appearance. A systematic look at the leaves, bark, twigs, and fruit provides a reliable guide to distinguish hickory from similar hardwoods like ash or walnut.
Identifying Features of Hickory Leaves
Hickory trees possess pinnately compound leaves, meaning multiple leaflets are arranged along a central stalk, known as a rachis. This structure differentiates hickory from trees with simple, undivided leaves. The leaves are arranged alternately along the twig, which helps distinguish hickory from the ash tree, which has an opposite leaf arrangement.
The number of leaflets per leaf varies between species, typically ranging from five to 17. The terminal leaflet, the one at the very tip of the rachis, is often noticeably larger than the lateral leaflets closer to the base. Leaflet shape is generally lanceolate or ovate, and the edges are finely serrated or toothed. The leaf stalk, or petiole, on some hickories, such as the Shagbark, can be quite stout.
Analyzing the Bark and Trunk
The bark of a mature hickory tree is one of its most recognizable features, though its appearance differs significantly between species. In younger trees, the bark is generally smooth and grayish-brown, often developing shallow vertical grooves. As the tree ages, the bark texture becomes diagnostic, often forming deep, interwoven ridges and furrows.
The Shagbark (Carya ovata) and Shellbark (Carya laciniosa) hickories are known for their distinct bark. On these species, the bark separates from the trunk and peels away in long, thick, vertical strips that curl outward, giving the trunk a characteristic “shaggy” look. In contrast, species like Mockernut (Carya tomentosa) and Pignut (Carya glabra) retain a tighter, more ridged bark that may be scaly or deeply furrowed but does not peel into exfoliating strips.
Diagnostic Twig and Bud Characteristics
Twigs on hickory trees are characteristically stout, often thicker than those of many other deciduous species. This stoutness is noticeable when examining the tree in winter, after the leaves have dropped. A primary identifying feature is the presence of a large terminal bud, which sits at the tip of the twig and is typically larger than the lateral buds.
These terminal buds are often ovoid or oblong in shape and can be up to three-quarters of an inch long. The arrangement and appearance of the protective bud scales also help with identification. For instance, the buds of many true hickories, like Shagbark, have numerous overlapping scales, a pattern known as imbricate. However, the Bitternut hickory (Carya cordiformis) is an exception, having a distinctive sulfur-yellow terminal bud with only two valvate scales that meet without overlapping.
The Role of Nuts and Husks
Hickory trees produce a fruit that is a hard nut encased within a thick, woody outer shell, or husk. The fruit is generally round or oval and its structure serves as a final confirmatory step in identification. When the fruit ripens in the fall, the husk splits open along defined lines, typically into four distinct segments or valves, to release the nut inside.
The size and thickness of the shell provide clues for species differentiation. The Mockernut hickory is known for its hard, thick shell, which surrounds a relatively small kernel. Conversely, the Pecan (Carya illinoinensis), a hickory species, is recognized for its thin shell. The nuts often have four distinct lengthwise ridges or ribs, and they are an important food source for wildlife.