Willows vary in size from large, spreading trees to creeping varieties. The 300 species of willow are mainly native to northern parts of the temperate world. The willow is part of the Salicaceae family, which includes poplars, aspens and cottonwoods. Willow trees include the Pacific willow, black willow and the sandbar willow.
The Pacific willow, also called the Western shining willow, is found along streams, lakes and elevations up to 8,500 feet on the West coast from California in the south and into Canada in the north, according to the "The Illustrated Encyclopedia of Trees of the World," by Tony Russell, Catherine Cutler and Martin Walters. The tree ranges in height from 15 to 45 feet with a diameter ranging from 1 to 2 feet. The trunk is slender. The bark is brownish-gray with deep furrows. The glossy green leaves are thin and spear shaped. The flowers are catkins---long thing flowers---that bloom in the spring.
The black willow is found from eastern and central North America into northern Mexico. The tree is harvested in the Mississippi delta region for timber, according to "Field Guide to Trees of North America" by National Geographic. The tree reaches a height of 100 feet. The bark is very dark, almost black, and becomes deeply grooved as the tree ages. The green leaves are thin and while rounded at the base, narrow to a point. Male and female catkins appear on the same tree in the spring.
East of the Rockies, the sandbar willow is a small tree or shrub. West of the Rockies, the willow grows as a many-stemmed thicket, according to "Field Guide to Trees of North America" by the National Wildlife Federation. The tree is found in sandbars, along the banks of streams and in silt flats, up to 5,800 feet in elevation. The leaves are very long and thin with a pointed tip. They are green with a gray tint. The flowers are catkins that bloom in the spring.