Common North American Trees with Pinnate Leaves

Common North American Trees with Pinnate Leaves

Pinnately compound leaves will have leaf stems called petioles that can have different lengths and connect the leaf to tree twigs. From the leaf's petiole connection to the first sub-leaf is an angle called an axil. This axil is always associated with a protruding axillary bud that will be the beginning of a new twig.

The pinnate leaf's extension above this growth bud will support 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.

Interestingly, some pinnately compound leaves can branch again and will 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 extra shoot systems and can confuse the leaf identification beginner. If your tree has a leaf that is pinnately compound, the leaflets are growing opposite each other in rows and do not have a bud in the leaflet axil, you should assume the leaf is pinnate or multi pinnate. 

If you have a leaf with these characteristics, you probably have a broadleaf or deciduous tree that is either an ash, hickory, walnut, pecan, box elder or black locust. The leaf structure on some of these hardwoods is very similar (exception are locusts and boxelder) but different enough to identify the tree to a major classification (genus).

Here are the most common trees that have pinnate leaves.

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The Major Hickories

Shagbark Hickory - Carya ovata A Shagbark
MichaelMattner/E+/Getty Images

In hickory trees, your tree will have a leaf with less than 9 leaflets and an alternate leaf arrangement. There is always a terminal leaf with 3 end or top leaflets that is 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 Hickories

 

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The Major Ashes

White Ash. White Ash

In ash trees, your tree will have a leaf with opposite leaf arrangement. There is always a terminal leaflet where leaflets (mostly 7 leaflets) are similar in size and shape.

Identification Tips: Ash trees have no nuts but clusters of slender seed 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.

The Major Ashes

 

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Walnut and Butternut

Black Walnut. Black Walnut

In black walnut and butternut trees, the true leaves will have an alternate leaf arrangement. Your tree will have a terminal leaflet with 9 to 21 broadly lance-shaped leaflets. 

Identification Tip: Check for fallen walnut fruit that is larger than hickory nuts. The husks do not split and completely wrap the nut.

Walnut and Butternut

 

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Pecan

Pecan. Pecan

In pecan trees, the true leaves will have an alternate leaf arrangement. Your tree will have a terminal leaflet with 11-17 slightly sickle-shaped leaflets.

Identification Tip: You rarely see wild pecan but you will see naturalized pecan and their nuts in pockets in the Southeastern U.S. states. The sickle-shaped leaflet is distinctive. 

Pecan

 

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Black Locust

Black Locust
Photo by Kim Nix

In black locust, your tree will have a leaf with 7-19 elliptic  leaflets and an alternate leaf arrangement. The tree will have short stout paired spines on branches at the leaf node attachment. 

Identification Tips: 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.

Black Locust

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Boxelder

Acer negundo
Boxelder in the Maple Family. Melissa McMasters/Flickr

The box elder is actually a maple with pinnate leaf structure. Your tree will have three maple-like leaflets (including a terminal leaflet) in the spring and five leaflets in summer. The leaflet margins are coarsely toothed.

Identification Tips: Boxelder is the only North American maple with pinnately compound leaves.

Boxelder