Getting Started with Tree Identification      

Identifying trees is a worthwhile goal for anyone. Beyond the satisfaction of simply knowing what tree you have, proper identification is a necessary step when trying to identify diseases or insect pests that may be affecting your tree.

For the novice, it’s easiest to identify trees during the growing season, when the leaves are on. Obviously, forestry professionals work all year long, so they look at the bark, leaf scars, buds, stem color, growth form, where the tree is growing, and other clues to determine the species. Today, we’ll concentrate on leaves for the novice learner.

One of the first steps in identifying hardwood trees is to determine whether the leaves are arranged alternately or opposite on the stem. Leaves are attached to the stem at a node, or a swollen area on the stem. Trees with oppositely arranged leaves have two leaves opposite each other arising from each node. Examples are maples and flowering dogwood. For alternately-arranged leaves, only one leaf grows from the node on one side of the stem, then at the next node the leaf is on the other side. Many Indiana hardwoods are in this category. We have one native tree with a whorled arrangement at each node (3 leaves per node), the Northern catalpa.

The next step is to determine the type of leaf: simple, compound, or doubly-compound. The description of a simple leaf is simple: a single leaf blade on a leaf stem (or petiole), like our state tree, the tuliptree. Compound leaves have 3 or more leaflets on the leaf stem. Examples are black walnut and hickories. Doubly-compound leaves are twice-compound, with branched leaf stems and a compound arrangement of leaflets on each “branch.” Examples include honeylocust and Kentucky coffeetree.

Simple leaves come in all shapes and sizes. For identification purposes, we look at the margin (the edge of the leaf), the shape, the size of the leaf, the lobes, and the length of the leaf stem.

There are a number of terms for leaf margins, but I’ll cover just a few basic types. An “entire” margin means the leaf edge is smooth. Toothed margins look like little teeth on a saw blade. Further, teeth can be classified as singly-toothed (singly serrate; evenly-sized teeth) or doubly-toothed (doubly serrate; with larger teeth and smaller teeth).

Lobed leaves have areas of the leaf that stick out (think of your ear lobe). These lobes may be rounded or pointed. Additional margin types include dentate (coarsely toothed), crenate (round-toothed), undulate (wavy), and others.

Leaf stems will vary from short to long. On compound leaves, each leaflet may have a short leaf stem, or it may be “sessile.” The base of sessile leaflets attaches directly to the leaf stem, or rachis, the extension of the petiole that bears the leaflets.

If the tree is old enough to produce fruit (called “mast”), characteristics of that fruit provide excellent clues as to the tree’s species. Fruit is classified as hard mast (hard-shelled seeds and nuts) or soft mast (fleshy, soft fruits).

An understanding of these basic terms will enable you to utilize a good tree identification book. There are many excellent books on the market. A good first resource for novice tree sleuths is Purdue Extension’s “An Introduction to Trees of Indiana,” available at the Education Store, https://edustore.purdue.edu.

Additionally, smartphone apps continue to improve. These may accurately identify a tree, but also may be in error, needing further investigation or cross-reference with a reliable tree identification book.

If short videos are more desirable for you, search on YouTube for videos by Purdue Extension Forester, Lenny Farlee, entitled “ID That Tree.”

Identifying needle evergreens is another discussion we’ll try to tackle in a future article.