Aspen

Populus adenopoda Populus alba Populus grandidentata Populus sieboldii Populus tremula Populus tremuloides

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 atypical, and one hybrid:

Populus adenopoda: Chinese Aspen Populus sieboldii: Japanese Aspen Populus alba: White Poplar Populus ? canescens: Grey Poplar Populus tremula: Common, Swedish, Trembling or Eurasian Aspen Populus tremuloides: Quaking, Trembling or American Aspen Populus grandidentata: Bigtooth Aspen Leaves

The Quaking Aspen of North America is known for its leaves turning spectacular tints of red and yellow in the autumn of the year . This causes forests of aspen trees to be noted tourist attractions for viewing them in the fall. These aspens are found as far south as the San Bernardino Mountains of Southern California, though they are most famous for growing in Colorado.

Aspens, apart from the aberrant White Poplar, are distinguished by their nearly round leaves on mature trees, 9–16 centimeters in diameter with irregular rounded teeth. They are carried on strongly flattened leaf stems, that cause the leaves to twist and flutter in slight breezes. The juvenile leaves on young seedlings and root sprouts differ markedly from the adult leaves, being nearly triangular, showing here the typical leaf shape of most other poplars; they are also often much larger, 13–26 cm long. The five typical aspens are distinguished from each other by leaf size and the size and spacing of the teeth on the adult leaves. White Poplar leaves differ in being deeply five-lobed, covered in thick white down, and having only a slightly flattened leaf stem. Habitat and longevity

The five typical aspens are all native to cold regions with cool summers, in the north of the Northern Hemisphere, extending south at high altitudes in the mountains. The White Poplar, by contrast, is native to warmer regions, with hot, dry summers