Willow

Willow, common name for a small family of woody flowering plants, and for certain trees of its representative genera. The willow family comprises about 435 species of willows and poplars (see Poplar), including the aspens and the cottonwoods. Members of the family usually live in moist habitats and in floodplains and riverbanks; they are rapid-growing, often pioneer, species. Their wood is used in many ways, and their leaves supply food for wildlife. Some species are ornamental. The family contains two genera: willow and poplar. Both are widespread in the northern hemisphere; a few species occur in the southern hemisphere. The 35 or so species of poplar are trees, and the majority of the 400 or so species of willow are shrubs. Willows are particularly abundant and important in the Arctic tundra, where they are low and matlike; they are also found above the timberline on mountains.

Willows and poplars produce male and female flowers on separate plants. The flowers are very simple, lacking both sepals and petals. They appear in dense clusters, called catkins, before or during the growth of new leaves in the spring. The catkins of poplars are pendent and produce no nectar; wind is the agent of pollination. The catkins of willows, in contrast, are erect and produce abundant, scented nectar that attracts insects, especially bees and moths, which carry out pollination. Insect pollination of the highly simplified flowers of willows is an exception to the rule in the plant kingdom that only plant groups with complex, showy flowers have their pollen distributed by insects. In the early spring, however, before most other flowers appear, insects rely on the nectar of willow catkins as a food source.

The fruits of willows and poplars are small capsules containing numerous seeds, each of which has cottonlike threads that act as parachutes, aiding in wind dispersal. If the seeds land on proper, moist soil, they germinate within one or two days. Most willows and poplars grow rapidly, reaching flowering age within a few years, but they are short-lived, some lasting only 20 years.

The economic importance of the family varies. Twigs of the common osier are grown for use in basketmaking, and the light but dent-resistant wood of other willows is used for artificial limbs, wooden shoes, and cricket bats. Willow bark contains the active compound salicin, used in many folk medicines. Aspirin is a derivative of salicylic acid, which was first synthesized from derivatives of willow bark. Several willows, such as weeping willow and pussywillow, are of horticultural importance.

Scientific classification: Willows make up the family Salicaceae. The willow genus is Salix, and the poplar genus is Populus. The common osier is classified as Salix viminalis, the weeping willow as Salix babylonica, and the pussywillow as Salix discolor.