Defining the characteristics of individual leaves is part of tree morphology, or the study of the physiological structure of trees. All trees have a leaf structure that can be classified as either simple or compound. Compound leaves can be classified further as pinnately compound, double or bi-pinnately compound, or palmately compound.
Identifying which category a tree leaf falls into can give you a better idea of what kind of tree you are observing. This guide provides key information on the differences between simple and compound leaves.

Simple Leaves
Simple leaves are singular units, attached to twigs by their stems or petioles. The margin of a simple leaf may vary, exhibiting smooth, jagged, lobed, or parted edges. Common North American trees like maple, sycamore, and sweet gum boast simple leaf structures.

Compound Leaves
In contrast to simple leaves, compound leaves consist of leaflets attached to a central vein with individual stalks. Imagine a cluster of single leaves attached to a central stem, known as a rachis, which, in turn, connects to a twig.
Differentiating between leaves and leaflets can be challenging. However, examining lateral buds along twigs or branches can aid in identification. Compound leaves exhibit bud nodes at the base of each stem or petiole but lack bud nodes at the base of each leaflet.
Types of Compound Leaves

Pinnately Compound
Pinnately compound leaves feature leaflets arising from both sides of the rachis. Three types of pinnate leaflet arrangements include even-pinnate, odd-pinnate, and alternate-pinnate, each defining leaflet morphology and aiding biologists in species identification.
Noteworthy pinnately compound trees in North America include hickory, walnut, pecan, ash, box elder, and black locust.

Double Pinnately Compound
Also known as bi-pinnate or twice pinnate, this leaf arrangement showcases leaflets arranged on secondary stems stemming from the rachis. While relatively rare among common North American trees, examples include honey locust, mimosa, Kentucky coffeetree, and Hercules club.

Palmately Compound
Palmately compound leaves resemble palm fronds, featuring leaflets radiating from a central attachment to the petiole. Buckeye and horse chestnut trees are native to North America and exhibit palmately compound leaves.
Frequently Asked Questions
What is a simple leaf? A simple leaf is a singular unit not divided into smaller leaflets, attached to the petiole as one entity.
Which leaves are called simple leaves? Examples of trees with simple leaves include maple, sycamore, and sweet gum.
What is a compound leaf? Compound leaves comprise multiple leaflets with individual stalks, all attached to the main stem.
Understanding the distinction between simple and compound tree leaves is crucial for botanists, arborists, and enthusiasts alike. By recognizing the unique characteristics of each leaf type, one gains deeper insights into tree identification and morphology.