Most people instantly recognize trembling aspen when the breeze picks up. The leaf stalk is flattened and longer than the leaf blade, and the slightest breeze causes the leaves to flutter. Young bark is smooth, pale grayish-white with horizontal lines, eventually growing dark and furrowed with age. The fluffy seeds are dispersed from hanging green capsules in late spring. Trembling aspen often grows in pure stands after disturbance, and succession will occur when young conifers or hardwoods seedlings take shelter and outgrow them.