The willow oak is native to the southeastern U.S. Its leaves somewhat resemble the willow and its preferred siting is along streams and rivers like the willow. It has a relatively shallow root system, which makes it more easily transplanted than many other oaks. The willow oak produces acorns biennially.

The genus Quercus includes more than 600 species of the oak tree, of which 90 are native to North America; the Chicago Botanic Garden's collection contains more than 60 varieties and over 1,000 individual trees. Twenty oak species are native to Illinois.

Oaks are slow growing, long lived, hard wood trees that produce fruit we all know as acorns. Within the white oak group, acorns mature annually; in the red oak group, acorns take two years to mature (biennial). Oaks are often imposing shade trees at maturity and provide habitat and food for a variety of wildlife.