Populus tremuloides

Individual clonal stands can be seen during the autumn, as on this mountainside in the Matanuska Valley in Alaska.

P. tremuloides leaves on mature trees are nearly round, 4–8 centimetres (1.6–3.1 in) in diameter with small rounded teeth, and a 3–7 centimetres (1.2–2.8 in) long, flattened petiole.

P. tremula leaves: adult (left) and juvenile (right)

Male catkins of Populus × canadensis

Aspens are a type of poplar tree with leaves that move with the slightest wind. The two main species are both called 'trembling aspens' or 'quaking aspens' on account of their leaves.

Some, but not all, are classified by botanists in the section Populus.