The oak trees in North America include many species, with some of these being hybrids and shrubs that occur only in localized regions. The oaks possess alternate leaves, with a single leaf existing at each node--the spot on the twig where the leaf attaches. You can use the shape of an oak leaf to differentiate among the many types. Focus your attention on such aspects of the oak leaf's shape as the number of nodes on the leaf and the indented areas between these, called sinuses.
Count the number of lobes on an oak leaf and you will get a general idea what type of oak a tree is and what kind it cannot be. For example, "Trees of North America" states that the bur oak has from five to nine lobes on each leaf, while a white oak has from seven to 11. If you found that a particular oak has leaves with five separate lobes, you can deduce that it cannot be a white oak, but that it could be a bur oak. Some oaks have many lobes, such as California white oak and Gambel oak, with as many as 11. Others have fewer lobes, like the three to seven lobes on a southern red oak leaf.
Examine the oak leaves with lobes carefully and classify the lobes as pointed or as rounded. Those species of oaks with pointed lobes include pin oak, northern red oak, scarlet oak and Shumard oak. The oaks with rounded lobes are types like the post oak, overcup oak, white oak and Chapman oak.
Look at the oaks that have no lobes on their leaves. These species include the live oak, the canyon live oak, the silverleaf oak, shingle oak and laurel oak. The leaves of these oaks will be oblong like on a shingle oak, elongated and narrow like those of willow oak or oval like a myrtle oak's are.
Inspect the depth of the sinuses between each lobe to distinguish oak species from each other. Some will have sinuses of various depths, like a white oak, with some not extending deep into the leaf and others coming close to the leaf's midrib area. Other oaks will have deep sinuses, such as nuttall oak and southern red oak.
Observe the edges of oak leaves, checking for serrations along the border of the leaf. Some oaks with single-bladed leaves that feature no lobes will have obvious rounded or pointed teeth all along their edges. Oaks of this nature include the chestnut oak, chinkapin oak, swamp white oak and the swamp chestnut oak.
Check for odd-shaped oak leaves that do not quite fall into any of the other categories. One would be the water oak, with leaves that resemble a rounded kite. Another is the blackjack oak, with a narrow base but a very wide apex.