Hickory trees in the United States grow mostly in the eastern part of the nation. The trees include such species as shagbark hickory, pignut hickory, bitternut hickory and the pecan. All of the hickory types produce an edible nut, and all have compound leaves that consist of a long stem that small leaflets grow on. These hickory leaves, though, vary in appearance among species.
When you consider the size of a hickory leaf, take into account the individual leaflets and the length of the stem they're attached to. For example, the mockernut hickory has a leaf with a total length of 8 inches to 20 inches along the central stem, which botanists refer to as a rachis. The individual leaflets are 2 inches to 8 inches long. Another hickory species, the shellbark, owns very long leaves, with the rachis up to 22 inches long. But the individual leaflets rarely are longer than 8 inches. Bitternut hickory has a relatively short rachis that is 6 inches to 9 inches long.
Number of Leaflets
Another factor in identifying hickory leaves is the total number of leaflets on the leaves of each species. For instance, pecans can have as many as 17 separate leaflets on one stem and typically have no fewer than nine. Conversely, shagbark hickory and pignut hickory normally have only five leaflets.
Odd Pinnately Compound
You will always find an odd number of leaflets on a hickory leaf. The correct term for describing hickory leaves is "odd pinnately compound," which describes an odd number of leaflets growing in rows opposite each other on the rachis. Because of the odd number of leaflets, one leaflet will be at the very end of the rachis growing by itself straight out from the terminal part of the stem.
Shape and Serrations
Hickory leaflets vary in shape. Those of the shagbark hickory look like the heads of lances, with a narrow base and an end that tapers to a point and being broadest in the middle. Water hickory has a much narrower leaflet that curves toward the end. The leaflets on a pecan tree have a much more pointed appearance at the ends.
The edges of hickory leaves also differ. Some have very fine "teeth," such as the serrations on water hickory leaflets. Others have more pronounced serrations along the leaf margins, such as shagbark hickory.
Hickory leaves are all a shade of green, with the exact hue depending on the species. Those of the shagbark hickory are a yellowish-green color, while black hickory features shiny, dark green leaves. Nutmeg hickory has a leaflet with a dark green upper surface but a whitish lower surface.
Fall colors of hickory leaves are usually some form of yellow. Pecan and pignut leaves change to yellow in the fall, according to the "National Audubon Field Guide to Trees." Shellbark hickory might turn a dull brown-yellow in fall but sometimes can produce a vivid display of golden leaves.