Red oak, black oak and bur oak have places where their ranges overlap in the eastern United States, and telling them apart can be a difficult proposition. Red oak (Quercus rubra) and black oak (Quercus velutina) grow in most of the East, while bur oak (Quercus macrocarpa) exists around the Great Lakes and into the lower and upper portions of the Midwest. Focusing on the variations in their leaves, acorns and bark can allow you to determine which of these oak species is which.
Step back and get a look at the height and spread of these three oak species. According to the Ohio Department of Natural Resources, all three oaks grow to different maximum heights and possess varying widths at their tops. The red oak will be about 60 feet tall and 70 feet wide in the open. Black oak reaches 60 feet high and is about that wide at its very top. The bur oak is more massive, growing as tall as 80 feet and having a spread of up to 90 feet. While you may not distinguish a red oak from a black oak this way, you should be able to discern that the bur oak is larger.
Examine the leaves of all three oaks, looking for disparities in their sizes and shapes. Red oak leaves will be from 5 to 8 inches long and 4 to 6 inches wide at their broadest point, with from seven to 11 lobes that end in bristly points. Black oak leaves are from 4 to 10 inches long and 3 to 6 inches wide, with between seven and nine pointed lobes. Bur oak leaves are much different from the other two types, having lengths of up to a foot and possessing as many as nine lobes, all rounded. The lobes closest to the stem are smaller than those at the very ends of the leaf.
Look for the autumn colors on the leaves of this trio of oaks. Red oak gets its name from the scarlet to deep red of its leaves in the fall, although some may have hints of golden brown. Black oak trees turn a range of colors in the fall, with some going to yellow and other trees going to red. Bur oak is the least impressive of these three, changing to chartreuse or a yellow-brown.
Study the acorns of these species and look for the differences in their sizes and their caps. Red oak’s acorns are from 3/4 of an inch to 1 inch long and have a cap resembling a saucer on their tops. The acorns are the smallest on a black oak when compared to the other two kinds, only 1/2-inch long at most and with a deeper cap. Bur oak’s acorns reach an 1-1/2 inches long and the frilly cap covers them for half this length.
Observe the colors and textures of the bark on these oak trees. Notice that the bark of red oak, when the tree is young, is light gray and quite smooth. The red oak retains its gray color when it's older and develops ridges in its bark. Black oak acquired its name for its dark gray to almost black bark, which has deep ridges and many furrows. Bur oak’s dark gray bark has obvious ridges that can be seen even from a distance.