Aspen, deciduous, hardwood tree in genus Populus of Willow family. Trembling (quaking) aspen (P. tremuloides) and largetooth aspen (P. grandidentata) are native to Canada; the former, found from the treeline to northern Mexico, is the most widely distributed tree in North America. Trembling aspen grows on most soils, doing best on well-drained, moist, sandy or gravelly loams. It is shade-intolerant and short-lived (about 60 years). A "pioneer" tree, it colonizes areas disturbed by logging or fire, propagating by root suckers rather than seeds. It also acts as "nurse tree" to softwood or hardwood forest taking over a site. On the Prairies, it may be the only tree.

Leaves are nearly circular, with a short tip; the flattened stalk makes them tremble in the wind. Twigs are slender, shiny and brownish grey, the bark smooth, waxy and pale green to chalky white in colour. Trees reach 12-18 m in height. Open grown specimens have a profusely branched, globular crown; forest trees have long, cylindrical trunks with short, rounded crowns.