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It's Leaf Season, So Take Some Time To Study Up

Updated: Oct 13, 2021

Autumn is here, and the leaves on our deciduous trees are changing colors and falling! It is a great time to collect these leaves and learn about them.

(Photo courtesy of Tyler Keene)

Leaves come in a variety of shapes, sizes, colors, textures and more. Let’s learn some of these features and the words scientists use to describe leaves.

Deciduous or evergreen?

Deciduous refers to trees that shed their leaves annually. These trees are usually broadleaf and have leaves that are flat and thin. Evergreen trees, just like the name implies, tend to keep their leaves and stay green even during chilly autumns and cold winters. These trees are typically coniferous with needles or scales.

Simple or compound?

Leaves from left: Maple. (Photo by A. Rafac) Virginia creeper (Photo by A. Rafac) Black walnut (Photo via Shutterstock)

A simple leaf has one blade and one leaf stalk. A compound leaf is made up of multiple blades attaching to one leaf stalk. Each individual blade of a compound leaf is called a leaflet. If the leaflets all attach to the leafstalk at the same point, it is called a palmately compound leaf. If the leaflets attach along different spots on the leafstalk, it is called pinnately compound.


Leaves from left: Linden and cottonwood. (Photos via Shutterstock)

The basswood (also called linden) leaf is heart shaped, and the cottonwood leaf is triangular. Or you could say both leaves have pointed tips, but the base of the basswood is indented while the base of the cottonwood is flat.

Some shapes can be simple to identify. Is it circular, triangular or heart-shaped? You can also look separately at the top and bottom of a leaf. What shapes do you see at the tip and the base of the leaf? Tips can be pointed, blunt, rounded or notched. Bases can be asymmetrical, indented, straight or tapered.

This red oak leak has many lobes that stick out and sinuses that curve in. (Photo by Angela Rafac)

Some leaves, like those from many oak and maple trees, have shapes that go in and out as you trace along the edges. The parts that stick out are called lobes, just like our earlobes stick out. The parts that go in are called sinuses, like the holes in our noses go in and lead to our sinuses.

Smooth or toothed margins

Leaves from left: Eastern redbud and slippery elm. (Photos by Angela Rafac)

There are also differences in the margins, or edges, of leaves. Does the leaf have smooth edges or are they notched? An edge with notches is called toothed. A toothed edge could be pointy or rounded. If there is a pattern with different-sized notches on a leaf, that leaf is said to be double toothed.

The Arbor Day Foundation has an awesome online key to help you identify trees by looking at their leaves. You can also learn even more leaf terminology.

Remember, it is illegal to pick or collect anything from the forest preserves, even if it is just a fallen leaf. Why? Fallen leaves provide homes, hiding spots, food and warm places for many forest animals.


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