Trembling aspen is a native and opportunistic species ready to colonize recently disturbed (cut, burned, or flooded) sites, so it's well represented along the lake trail. As the photo indicates, trembling aspen leaves are nearly round (in fact, medallion-like) and finely toothed. They're also ready to flutter in the mildest of breezes because, as Norman Smith says, "the petioles or leaf-stems are flattened perpendicular to the leaf blade, ideal for catching the wind" (34).