The Common Oaks - The Major Quercus Tree Species of North America

Oak Trees in the Beech of Fagaceae Family

Swamp Chestnut Oak
Swamp Chestnut Oak. Photo by Steve Nix

The term oak can be used as part of the common name of any of about 400 species of oak trees and shrubs in the genus Quercus (from Latin "oak tree). The genus quercus is native to the northern hemisphere and includes deciduous and even evergreen species extending from cold latitudes to tropical Asia and the Americas.

Oaks have spirally arranged leaves, with a lobed margin in many species. Other oak species have serrated (toothed) leaves or have smooth leaf margins which are also called entire leaves.

Oak flowers are catkins and are seen falling in late spring. That flower's fruit is a nut called an acorn, borne in a cup-like structure known as a cupule. Every acorn contains one seed (rarely two or three) and takes 6-18 months to mature, depending on species.

The "live oaks" (oaks with evergreen or extremely persistent leaves) are not necessarily a distinct group their members are scattered among the species below.

The Common North American Oak Species

Summer Oak Identification:

  • Leaves: alternate, variable in shape, short-stalked.
  • Bark: gray and scaly or blackish and furrowed.
  • Twigs: slender with star-shaped pith.
  • Fruit: acorns.

Dormant Oak Identification:

Oak has a 5-sided pith so cut into a small stem for inspection; has variable bark so not very helpful for identification; has clustered buds at tip of twig and very important for identification; has persistent leaves on live and water oak; has slightly raised, semi-circular leaf scars; has numerous bundle scars; has acorns persistent on twigs or dropped under the tree.