Why Are Oak Trees So Hard to Identify?

The acorns and leaves of many oak species closely resemble each other.

Oak trees (Quercus family) are difficult to distinguish from each other because of similarities in features. The oaks that lose their leaves in the fall -- the deciduous oaks -- often resemble each other, while the evergreen oaks usually share common traits.

Geography

In North America, the ranges of different oak species often overlap, adding to the confusion of which oak tree is which. In the East, for example, the geographic distributions of oaks such as white oak (Quercus alba), bur oak (Quercus macrocarpa), post oak (Quercus stellata), northern red oak (Quercus rubra), pin oak (Quercus palustris) and black oak (Quercus velutina) all coincide.

Leaves

The foliage on many oaks is comparable, with slight differences in size, color and shape of the leaves existing between species. Northern red oak leaves look like those of black oak, except for disparity between the two species in the number of separate sections, called lobes, which each leaf possesses. Interior live oak (Quercus wislizenii) has almost the same type of foliage as California live oak (Quercus agrifolia), except they are smaller.

Identification

Oaks produce a fruit called an acorn, with the acorns of many oaks closely emulating one another. Keen observation of the shape, size, color, cap and how the acorns grow on the branches help differentiate species.

References

• University of Connecticut Plant Database: Quercus Rubra
• University of Connecticut Plant Database: Quercus Macrocarpa
• University of Connecticut Plant Database: Quercus Palustris
• University of Connecticut Plant Database: Quercus Alba
• "Trees of North America"; C. Frank Brockman; Revised 1986 (Pages 120 through 134)
• "National Audubon Society Field Guide to Trees: Eastern Region"; Elbert L. Little, Revised 2008 (Pages 382 through 411)