People ask this one a lot, and the honest answer is “yes and no.” Aspens are a kind of poplar, so every aspen is a poplar. But the word “poplar” also covers cottonwoods, white poplar, Lombardy poplar and a long list of hybrids, and those trees look and behave quite differently from an aspen. Once you know what to look at, telling them apart is not hard.

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The short answer: aspens and poplars belong to the same genus, Populus, in the willow family. Quaking aspen is one species of poplar. Other poplars include eastern cottonwood and white poplar. Aspens have small, nearly round leaves on flat stalks that tremble in the slightest breeze, and smooth, pale bark. Cottonwoods are much bigger trees with triangular leaves and thick, deeply furrowed bark. White poplar has lobed leaves that are bright white underneath.

One genus, many trees

All poplars and aspens sit in the genus Populus. The Morton Arboretum lists quaking aspen and eastern cottonwood in the willow family, Salicaceae, which is why they share some habits with willows: fast growth, soft wood, a liking for moisture and a tendency to sucker.

“Aspen” is a common name for a smaller group of Populus species with round leaves, flattened leaf stalks and smooth, light bark. In North America the familiar one is quaking aspen (Populus tremuloides). “Poplar” is used more loosely. Sometimes it means the whole genus, and sometimes it means the non-aspen members such as cottonwoods and white poplar.

One name to watch: “tulip poplar” (tuliptree) is not a poplar at all. It is a magnolia relative that happens to share the name.

Quick comparison

Feature	Quaking aspen	Eastern cottonwood	White poplar
Mature height	40 to 50 ft	75 to 100 ft	40 to 70 ft
Mature width	20 to 30 ft	50 to 75 ft	40 to 70 ft
Leaf shape	Oval to nearly round, finely toothed	Triangular with a pointed tip	Three to five lobes, white and hairy below
Young bark	Smooth, grayish white	Smooth, gray-green	Whitish with dark patches
Older bark	Furrowed, with darker areas	Ash-gray, thick, deeply furrowed and blocky	Ridged and furrowed, ridges turning black
Native?	Yes, northern North America	Yes, eastern North America	No, introduced

Sizes and descriptions from the Morton Arboretum.

Look at the leaves first

Aspen leaves

The Morton Arboretum describes quaking aspen leaves as oval to nearly round, 1 to 3 inches wide, with finely serrated edges. The key detail is the leaf stalk, which is flattened side to side. That flat stalk lets the leaf flutter in almost no wind, which gives the tree its name and its rustling sound. Fall color is bright yellow.

Cottonwood leaves

Eastern cottonwood leaves are larger, 2 to 5 inches long, and triangle-shaped with a toothed margin and an elongated tip. Their stalks are also flattened, so cottonwood leaves move in the wind too, but the shape is very different from an aspen’s coin-like leaf.

White poplar leaves

White poplar is the easiest to spot. Its leaves have three to five lobes, a little like a small maple leaf, and the undersides are white because of a thick coat of hairs. On a breezy day a white poplar flashes silver and green.

Then check the bark

Aspen bark is smooth and grayish white on young trees, and the Morton Arboretum notes that older trees become furrowed with darker areas. People sometimes mistake aspens for birches because of that pale bark; see birch vs. aspen for that comparison.

Cottonwood bark on a mature tree is ash-gray, thick and blocky, with deep furrows and ridges. You will not confuse an old cottonwood trunk with an aspen.

White poplar bark starts whitish with small dark patches and becomes ridged with age, the ridges turning black.

Size and setting

Aspens are medium to large trees, but cottonwoods are giants. The Morton Arboretum lists eastern cottonwood at 75 to 100 feet tall, usually along streams, rivers and lowland areas. If a poplar-type tree is towering over a riverbank, it is probably a cottonwood.

Quaking aspen is native to the northern part of North America and prefers cool summers. The Morton Arboretum notes it does not tolerate summer heat or pollution well, and it is short-lived. Aspens also sucker freely from their roots, so they often grow as groves of connected stems.

Why the difference matters in a yard

The differences go beyond looks.

Aspen is beautiful but often short-lived in hot or polluted sites, with many pest and disease problems when planted in the wrong place. It is highly susceptible to ice damage and suckers heavily. The Morton Arboretum recommends planting it in moist soil and full sun, as it does not tolerate shade.
Cottonwood grows very fast, but the Morton Arboretum warns about its large size, weak wood and roots prone to invading sewer pipes. It is best used on large properties away from homes. If you are thinking about root spread, our guide on how far a willow should be from a house covers a close relative with similar root habits.
White poplar is not native and suckers aggressively, so it is rarely a good planting choice today.

All of these trees share many pests with willows, including leaf beetles and aphids; the University of Kentucky’s willow pest guide lists several that move between willows, poplars and cottonwoods.

How to tell which one you have

Check the leaf shape. Round and small points to aspen. Triangular points to cottonwood. Lobed with a white underside points to white poplar.
Twist a leaf stalk. Flat stalks are typical of aspens and cottonwoods.
Look at older bark. Smooth and pale suggests aspen, while thick, deeply furrowed gray bark suggests cottonwood.
Think about size and site. A very large tree by water is most likely a cottonwood.
Look for groves. Many stems of similar size spread across an area often mean an aspen clone.

Choosing between them

If you are planting rather than identifying, the ISA’s tree selection advice applies: match the tree to the site, its mature size and its soil, and think about what is underground and overhead. Fast-growing poplars can fill a space quickly but rarely make long-lived yard trees. In many gardens a slower, sturdier tree is the better long-term choice.

For more help identifying trees, see the tree identification hub.

Sources

Quaking Aspen, The Morton Arboretum
Eastern Cottonwood, The Morton Arboretum
White Poplar, The Morton Arboretum
Common Insect Pests of Willow, University of Kentucky Entomology
Tree Selection, International Society of Arboriculture, TreesAreGood.org

Top photo: Tewy, CC BY-SA 3.0, via Wikimedia Commons

Are Poplar and Aspen Trees the Same?