How to identify a tree by its leaves, step by step

To identify a tree by its leaves, work through a short key in order: is it a needle or a broad leaf, is the leaf simple or compound, are the leaves opposite or alternate on the twig, are the edges smooth, toothed or lobed, and what is the overall shape? Each answer shortens the list, and together they usually point to a small group of candidates.

The order matters. Shape is what everyone looks at first, and on its own it is the least reliable, so leave it for last.

Before you start

• Look at several leaves, not one. Leaves on the same tree vary, and leaves grown in shade are often larger than those in full sun.
• Look at the twig as well as the leaf.
• Gather fallen leaves where you can rather than pulling them from the branch. In autumn the ground offers plenty.
• Never taste or eat any part of a wild plant to help identify it. Identifying by leaf is for knowing a tree, not for foraging.
• In North America, learn poison ivy before you go: three leaflets to a leaf, on a vine or low shrub. Do not touch it.

Step 1: needles, scales or broad leaves

• Needles, single or in bundles: a conifer such as a pine, spruce or fir.
• Tiny overlapping scales pressed against the twig: a conifer such as a cedar, cypress or juniper.
• A flat, broad blade: a broadleaf tree. Go on to step 2.

Step 2: simple or compound

This is the step most beginners miss. A simple leaf has one blade on its stalk. A compound leaf is divided into several separate leaflets on one stalk, and the whole set is a single leaf.

To tell them apart, find the bud. A true leaf has a small bud in the angle where its stalk meets the twig. A leaflet has no bud at its base.

• Simple: one blade, with a bud at the base of the stalk. Maples, oaks, birches, elms.
• Pinnately compound: leaflets in two rows along a central stalk, like a feather. Ash, walnut, hickory, black locust.
• Palmately compound: leaflets spreading from a single point, like fingers. Horse chestnut and buckeye.

Step 3: opposite or alternate

Now look at how the leaves are attached along the twig.

• Opposite: leaves grow in pairs, directly across from each other.
• Alternate: one leaf at each point, staggered up the twig.
• Whorled: three or more at one point. Uncommon in trees.

Opposite is the rarer pattern, which makes it the more useful one. Among common trees of temperate North America, a handy memory aid for opposite leaves is MAD Horse: maple, ash, dogwood and horse chestnut, along with its relative the buckeye. If your leaves are opposite, start with those. If they are alternate, the list is longer, and the next steps narrow it.

Check several twigs. A single damaged twig can mislead you.

Step 4: the edge

Run a finger gently along the edge of the leaf, which botanists call the margin.

• Entire: smooth, with no teeth. Dogwoods and magnolias.
• Toothed: small saw-like teeth all along. Cherries and many willows.
• Doubly toothed: large teeth carrying smaller teeth on them. Elms and birches often show this.
• Lobed: deep bays cut into the blade, with lobes between them. Oaks, maples, sweetgum, sycamore.

Lobes repay a closer look. Among oaks, lobes with bristle-pointed tips suggest the red oak group, while rounded lobes without bristles suggest the white oak group. And some trees refuse to choose: sassafras can carry unlobed, two-lobed and three-lobed leaves on the same tree, which is why one leaf is never enough.

Step 5: the shape

Last of all, the overall outline.

• Egg-shaped (ovate): broadest below the middle, tapering to the tip. Many cherries, birches and elms.
• Lance-shaped (lanceolate): long and narrow, tapering to a point. Many willows.
• Heart-shaped (cordate): notched where the stalk joins. Redbud and linden.
• Fan-shaped: the ginkgo, with its split fan, is hard to mistake.
• Star- or hand-shaped: lobes radiating from one point. Maples and sweetgum.

Note the base of the leaf as well. Elm leaves are often lopsided at the base, with one side reaching farther down the stalk than the other.

Putting the key together

Here is the key at work on two leaves.

• Leaf A: broad, simple, opposite, lobed, hand-shaped. Opposite rules out oaks and sweetgum; simple rules out ash and horse chestnut. A maple is the likely answer.
• Leaf B: broad, simple, alternate, lobed, with bristle tips on the lobes. Alternate leaves and bristle-tipped lobes point to an oak in the red oak group.

Then confirm with a field guide for your region, checking the bark, fruit and overall form of the tree. A key gets you to the right page; the details on that page finish the job.

Keep a leaf record

• Press one leaf from each tree flat between sheets of paper under heavy books for a week or two.
• Label it with the date, the place and your five answers.
• Add the name once you are sure, and a question mark until you are.

Over a season, the collection becomes your own field guide.

Good to know

Leaves change through the year, and a young tree or a vigorous shoot can carry leaves larger or oddly shaped compared with the rest. When the leaves have fallen, buds, bark and branching take over, and that is a key for another day.