Populus tremuloides

Populus tremuloides is a deciduous tree native to cooler areas of North America, one of several species referred to by the common name Aspen. It is commonly called quaking aspen, trembling aspen, American aspen, Quakies, mountain or golden aspen, trembling poplar, white poplar, popple, and even more names. The trees have tall trunks, up to 25 meters (82 feet) tall, with smooth pale bark, scarred with black. The glossy green leaves, dull beneath, become golden to yellow, rarely red, in autumn. The species often propagates through its roots to form large groves based on a single rhizome.

The Quaking Aspen is the most widely distributed tree in North America, being found from Canada to central Mexico. It is the defining species of the aspen parkland biome in the Prairie Provinces of Canada.

The quaking or trembling of the leaves that is referred to in the common names is due to the flexible flattened petioles. The specific epithet, tremuloides, means similar to Populus tremula, the European aspen. Some species of Populus have petioles flattened partially along their length, while the aspens and some other poplars have them flattened from side to side along the entire length of the petiole.

A tall, fast growing tree, usually 20–25 m (66–82 ft) at maturity, with a trunk 20–80 cm (0.66–2.62 ft) in diameter; records are 36.5 m (120 ft) in height and 1.37 m (4.5 ft) in diameter.
The bark is relatively smooth, colored greenish-white to gray, and is marked by thick black horizontal scars and prominent black knots. Parallel vertical scars are tell-tale signs of elk, which strip off aspen bark with their front teeth.

The leaves on mature trees are nearly round, 4–8 centimeters (1.6–3.1 in) in diameter with small rounded teeth, and a 3–7 centimeters (1.2–2.8 in) long, flattened petiole. Young trees (including root sprouts) have much larger—10–20 centimeters (3.9–7.9 in) long—nearly triangular leaves.
The flowers are catkins 4–6 centimeters (1.6–2.4 in) long, produced in early spring before the leaves; it is dioecious, with male and female catkins on different trees. The fruit is a 10-centimeter-long (3.9 in) pendulous string of 6-millimeter (0.24 in) capsules, each capsule containing about ten minute seeds embedded in cottony fluff, which aids wind dispersal of the seeds when they are mature in early summer.

The quaking aspen is the State Tree of Utah.