Willows are deciduous shrubs and trees in the genus Salix.
Leaves are usually narrow and long (lance-shaped or linear), with a rounded base and pointed tip, often with teeth along the margin.
Wood is often brittle, weak and prone to breakage in ice and strong winds (many willows are fast-growing, water-loving species).
Twigs are famously slender, tough and flexible, hence the phrase "bend like a willow." Many willows can be grown from cuttings, by simply sticking a willow branch into the soil.
Male and female flowers develop in separate catkins on separate plants (each willow tree bears either male catkins, or female catkins, but not both). (Catkins are spikelike, often cylindrical, sometimes pendulous, rather tightly packed clusters of unisexual flowers.) Willow catkins are often hairy.
Fruits are capsules (often conical and brown or reddish) that develop in the female catkins; each capsule is filled with tiny seeds, often with hairs at the base.