Willow, shrubs, and trees of the genus Salix, family Salicaceae, mostly native to north temperate areas and valued for ornament, shade, erosion control, and timber. Salicin, a source of salicylic acid used in pain relievers, is derived from certain willows. All species have alternate, usually narrow leaves and catkins, male and female on separate trees; the seeds have long, silky hairs.

Source: Britannica