The leaves of the hickory tree, belonging to the genus Carya, provide the visual clues for identification. Observing the foliage is the most reliable way to distinguish a hickory from similar trees, such as the walnut (Juglans). The arrangement, the number of individual leaf parts, and the subtle details of the edges and texture allow an observer to confidently identify a hickory tree in the landscape.
The Foundation: Hickory’s Compound Leaf Structure
Hickory trees possess compound leaves, a feature that immediately sets them apart from trees with simple leaves. A simple leaf consists of a single blade attached to the main stem, while a compound leaf is divided completely into multiple smaller segments called leaflets.
The hickory’s leaf arrangement is pinnately compound, meaning the leaflets are arranged in pairs along a central stalk known as the rachis. The compound leaves are attached to the twig in an alternate pattern, where only one leaf emerges at each node along the branch. This alternate positioning is a reliable identifier that helps rule out trees like the ash, which have a similar compound leaf structure but an opposite arrangement on the branch.
Leaflet Characteristics: Count, Shape, and Size
The number of leaflets on a hickory leaf ranges between five and 17 per compound leaf. Many of the “true hickories” show a lower number, typically five to seven leaflets. Pecan hickories, however, tend toward the higher end of this count, often possessing nine to 13, and sometimes up to 17, leaflets on a single rachis.
Many Carya species show a difference in size between the leaflets on the same leaf. The terminal leaflet, the single one at the tip of the rachis, is often noticeably larger than the lateral pairs below it. Leaflet shape generally ranges from lanceolate (long and narrow) to obovate (wider near the tip). The basal (lower) leaflets are usually the smallest. This graduation in size toward the tip is a strong visual cue for identification.
Detailed Identification: Margins, Texture, and Color
The margins, or edges, of hickory leaflets are nearly always toothed, ranging from finely to coarsely serrated depending on the specific species. This toothed edge is a consistent trait across most hickories and walnuts, so it must be examined in conjunction with the other characteristics.
Hickory leaves are typically medium to dark green and have a smooth surface on the upper side. The underside of the leaflet is often paler and may be covered in fine hairs (pubescence), particularly in species like the mockernut hickory (Carya tomentosa). In autumn, the foliage changes to shades of rich golden-yellow or bronze before they drop.