Flower:

Male and female flowers are on separate trees (dioecious) in hanging clusters (catkins) from the leaf axils of 1 year old branch twigs. Male catkins are 1 to 3½ inches long with tiers of red stamens. Female catkins are 1¼ to 3 inches long with red stigmas.

Leaves and stems:

Leaves are alternate and simple with a flat leaf stalk. The blade is 2 to 4 inches long and 1¾ to 3½ inches wide, oval to broadly egg-shaped, rounded or pointed at the tip, rounded at the base. Large, coarse, blunt teeth are all along the edges. Both leaf surfaces have white woolly hairs when emerging, the upper less so than below and turning smooth and dark green, the lower surface light green and shedding most of the hairs at maturity.

Twigs emerge dense, woolly white, turning greenish brown and partially to mostly hairless by end of summer. Buds are round, ¼ to 3/8 inch long and pointed, white from wooly hairs, reddish brown underneath. Bark is smooth and thin, green or yellowish gray on younger branches and the upper trunk. Older bark at the base of trunk becomes thick and dark gray/brown with coarse ridges and deep furrows.The trunk can get up to 24-inch diameter at breast height.

Fruit:

The fruits are green, narrowly round capsules densely arranged on the long pendulous catkins. The capsules split into two halves releasing the cottony seed.

Notes:

Bigtooth Aspen is a tall, narrow-crowned tree throughout most of Minnesota's upland forests. It's a clonal species that spreads by root suckers, though its colonies are much smaller and far less frequent than the similar Quaking Aspen (Populus tremuloides). Like Quaking Aspen, Bigtooth Aspen leaves have a flat stalk that causes the leaves to flutter in the wind, but its leaves are also more egg shaped with large, blunt teeth. Its bark is similar as well but it stays a darker greenish gray to nearly olive where Quaking Aspen's bark is a light greenish gray to nearly white. Bigtooth Aspen's fall color can be deep yellow but it can also display foliage that is deeply orange with tinges of red.