This genus consists of about 400 species of deciduous trees and shrubs. They are native primarily to the cooler, temperate regions of the Northern Hemisphere. The precursor to aspirin, salicylic acid, is found in the bark and leaves of willows.

Most of the members of this genus are trees but a few grow as shrubs. They tend to be fast growing and weak wooded. The weeping willow is noted for its ability to tolerate wet sites near ponds or streams.