Aspens are trees of the willow family and comprise a section of the poplar genus Populus sect. Populus. There are six species in the section, one of them somewhat atypical, and one hybrid:

• Populus tremula - Eurasian aspen (northern Europe & Asia)
• Populus tremuloides - American aspen (northern & western North America)
• Populus grandidentata - Bigtooth aspen (eastern North America, south of P. tremuloides)
• Populus adenopoda - Chinese aspen (China, south of P. tremula)
• Populus sieboldii - Japanese aspen (Japan)
• Populus alba - White poplar (southeast Europe & southwest Asia)
• Populus x canescens - Grey poplar (hybrid P. alba x P. tremula)

Cultural aspects

The aspen tree's quivering leaves are, in Christian lore, said to be the result of arrogance at the Crucifixion because the aspen did not tremble like other trees. A German version claims that the aspen was the only tree to refuse to acknowledge Jesus' divinity. The cross that Christ was crucified on is sometimes said to have been aspen wood. It is also sometimes said that aspen leaves are made from female tongues and their quivering is due to women's inability to stop talking.

• Aspen, Colorado is a ski-resort town in the United States of America.
• Aspen, Nova Scotia is a small community in Guysborough County.
• Aspen Hill, Maryland is also a place in the United States of America.