and pin oaks (Quercus palustris) both belong to the so-called red-oak group, trees and shrubs with bristle-tipped leaves. This distinguishes them from oaks in the white-oak group with rounded tips. Both red oak and pin oak are hardy within U.S. Department of Agriculture plant hardiness zones 4 through 8. Red oak has an extensive natural range in the eastern United States. The pin oak's native range is smaller, and almost entirely overlaps that of red oak. The exception is where pin oak reaches westward a bit more than red oak does into Oklahoma and Kansas. Both trees are planted outside their natural ranges.
Pin oaks and red oaks have leaves with lobes and sinuses. Lobes are the parts that extend outward from the leaf's midvein. Sinuses are the rounded, cove-shaped indentations between the lobes. Red oak leaves' sinuses are typically no deeper than halfway to the midvein, while those of the pin oak are deeper, often reaching close to the midvein. Red oak leaves generally have more lobes, between seven and 11 compared to pin oak's five to nine.
The pin oak's leaves are smaller -- between 3 and 6 inches long -- compared to red oak's 5- to 8-inch leaves. Both of these oaks have autumn leaf colors ranging from brown to red, then all brown in winter. In the growing season, red oak leaves are a dull green, sometimes tending toward blue-green, while pin oak leaves are a brighter green with more of a luster. Both are paler below than above and may have small tufts of hairs underneath where the leaf veins meet.
Red oak and pin oak acorns -- the oak tree's fruit -- may be similar in shape and proportion, with a shallow cup covering a quarter or less of the fruit. But there is a considerable size difference:
- Pin oak acorns measure 1/2 inch long on average
- Red oak acorns are typically between 3/4 inch and 1 inch, or even slightly larger.
Both have tightly-fitting scales on the acorn cup, but a close inspection will sometimes reveal that pin oak acorn scales are slightly hairy.
Form and Height
Pin Oak: Open-grown pin oak trees tend to have a distinctive form. Topmost branches ascend at an upward angle, middle branches are more or less horizontal and lower branches droop. Pin oaks generally also have a well-defined main trunk that extends in fairly straight form well up into the crown. Maximum heights of 75 feet are typical.
Red Oak: The red oak typically has a straight lower trunk that transitions into large, curving branches in the crown. It lacks the three different branch orientations characteristic of the pin oak. The red oak can reach 80 feet or more in the wild.
Twigs and Bark
Pin oak's twigs are considerably more slender than those of the red oak, and they have a bit of a varnished appearance that is generally lacking in red oak twigs. In keeping with the overall smaller dimensions, pin oak buds are on the order of 1/8 inch long, while those of red oak are closer to 1/4 inch. There's a slight amount of hairiness at the tip of red oak buds, whereas pin oak buds are all but hairless.
Dendrologists -- those who specialize in trees, shrubs and vines -- often describe red oak's mature bark as having furrows and flat ridges that are suggestive of ski trails. With a little imagination, this is an apt description. Pin oak, in contrast, has thin, tight bark with slight furrows and narrow ridges that lack the ski-trail feature of red oak.