The aspen is a type of tree from the genus Populus. These trees are known for their leaves that shake or tremble in even the lightest breeze. This trembling happens because the leaves have flat stems, which allows them to move easily when wind blows through them.
European aspen (Populus tremula) and quaking aspen (Populus tremuloides) are the most well-known aspens. A related species, Euphrates poplar (Populus euphratica), grows in the Middle East and may have been familiar to people in Bible times, particularly in regions near water sources.