Are you wondering which North American trees have pinnate leaves? Below, you’ll find out about the most common trees with a pinnated leaf structure—hickory, ash, walnut, and a few others—and learn how to identify them.
Pinnately compound leaves have stems (petioles) that vary in length and connect the leaf to the tree twigs. The axil is the angle from the leaf’s petiole connection to the first sub-leaf. This axil is always associated with a protruding axillary bud that is the beginning of a new twig.
The pinnate leaf’s extension above this growth bud supports opposing rows of smaller sub-leaves, which are called leaflets. These leaflets form on either side of an extension of the petiole called the midrib in a simple leaf or a rachis in multi-pinnate leaves.
Some pinnately compound leaves can branch again and develop a second set of pinnately compound leaflets. The botanical term for leaves with these secondary leaf branches is called a bipinnately compound leaf.
There are many degrees of “compoundness” in more complicated leaves (such as tripinnately compound). Leaf compoundness may cause these tree leaves to have extra shoot systems and can confuse the leaf identification beginner. If the tree you’re examining has a leaf that’s pinnately compound—the leaflets are growing opposite each other in rows and don’t have a bud in the leaflet axil—you should assume the leaf is pinnate or multi-pinnate.
If you’re examining a leaf with these characteristics, you probably have a broadleaf or deciduous tree that’s either an ash, hickory, walnut, pecan, box elder, or black locust. The leaf structure on some of these hardwoods is similar (exceptions are locusts and boxelder) but different enough to identify the tree to a major classification (genus). Read on to get a visual of the most common trees that have pinnate leaves.
The Major Hickories
Hickory trees have a leaf with less than nine leaflets and an alternate leaf arrangement. There’s always a terminal leaf with three end or top leaflets that’s distinctly larger than basal or bottom leaflets.
Identification Tips: Check for fallen hickory nuts that are much smaller than walnuts and encased in splitting husks. Check for an alternate leaf arrangement to eliminate ash, which is opposite in arrangement.
The Major Ashes
Ash trees have a leaf with opposite leaf arrangement. There’s always a terminal leaflet where leaflets (mostly seven leaflets) are similar in size and shape.
Identification Tips: Ash trees have no nuts but clusters of slender seeds with a long wing. There will be no nut husks under the tree. Check for an opposite leaf arrangement to eliminate hickory, which is alternate in leaf arrangement.
Walnut and Butternut
Black walnut and butternut tree leaves will have an alternate leaf arrangement. These trees will have a terminal leaflet with nine to 21 broadly lance-shaped leaflets.
Identification Tip: Check for fallen walnut fruit that’s larger than hickory nuts. The husks do not split and completely wrap the nut.
Pecan
Pecan tree leaves will have an alternate leaf arrangement. This tree has a terminal leaflet with 11 to 17 slightly sickle-shaped leaflets.
Identification Tip: You’ll rarely see wild pecan but will encounter naturalized pecan and its nuts in pockets in the Southeastern U.S. states. The sickle-shaped leaflet is distinctive.
Black Locust
Black locust trees have a leaf with seven to 19 elliptic leaflets and an alternate leaf arrangement. The tree has short stout paired spines on branches at the leaf node attachment.
Identification Tip: There will often be a long, wide, flattened fruit pod that can be persistent through early winter. These pods will have thin papery walls attached to twigs.
Boxelder
The boxelder is a maple with a pinnate leaf structure. This tree has three maple-like leaflets (including a terminal leaflet) in the spring and five leaflets in the summer. The leaflet margins are coarsely toothed.
Identification Tip: Boxelder is the only North American maple with pinnately compound leaves.