Leaf peepers: Clues to help identify white oaks
“There were many splendid oaks,” wrote John S. Wilcox in 1906, describing Kane County at the time of European settlement.
“Massive boles would square over two feet, which rose straight as arrows, with a height of thirty or forty feet to the first spreading branches which formed their lofty crowns.”
These magnificent trees included white oaks, red oaks, black oaks and bur oaks. There were swamp white oaks and chinkapin oaks, Hill’s oaks and shingle oaks, too. Although oaks are in serious decline, these species can still be found in Kane County.
Identifying oaks
“How can you tell which is which?” people often ask me, surprised to learn how many different oaks there are. Each species has some key features, and once you know what to look for, you’ll be able to identify the different oaks in our area.
For starters, pick up a few oak leaves and take a good look. Most oak leaves have lobes, or divisions. (One species doesn’t have lobed leaves, but we’ll save that for later.) Trees in the white oak group have rounded-lobed leaves. Trees in the red oak group have lobes that come to a pointed tip.
Within each major group of oaks, there are numerous species. In Kane County, the white oak group includes its namesake, the white oak, bur oak, and swamp white oak. Distinguishing these requires a little closer look.
Again, start with some leaves. White oak leaves are about 10 inches long, with seven to nine rounded lobes. The indentations between the lobes, called sinuses, can be shallow or deep. In autumn the leaves turn a rich red color.
Bur oak leaves, by contrast, are generally bigger and tougher looking than white oaks. The key feature to look for is the width of the leaves at the top (away from the leaf stalk).
Bur oak leaves are broad at one end, with shallow sinuses, and thin toward the stalk. One trick to bur oak identification is to look for the “witch.” If you hold the leaf upside down — broad end at the bottom, stalk at the top — and look at the outline of the leaf, you’ll see the silhouette of a witch.
Her pointed hat is at the top, her narrow waist is in the middle, and her billowing skirt is at the bottom of the leaf. This requires a bit of imagination, but pick up a burr oak leaf and give it a try.
The third species in the white oak group, swamp white oak, also has leaves that are broad at one end and narrow toward the stalk. They don’t narrow as abruptly as the bur oak leaves do. In swamp white oak, the sinuses are all shallow, and sometimes the shallow sinuses make the leaf look wavy rather than lobed.
Swamp white oak leaves are whitish on the underside, and green on the top. Hence, its scientific name, Quercus bicolor. You can often see the white and green when a breeze moves through the trees.
Acorn clues
Then, there are acorns. Sometimes lots and lots of acorns! Acorns are the fruit of the oak, and each species’ fruit is unique. The acorns are so different that you can identify a tree by the acorns alone.
In “mast” years, oaks produce prodigious numbers of acorns. Some years, there are very few. Pick up a few from different oaks and compare them. If you’ve got an acorn that’s about ¾ to 1 inch long with a shallow cap that looks “warty” (bumpy), it’s from a white oak.
These acorns are borne either singly or in pairs on the tree. As soon as they hit the ground, they’re ready to sprout. You’ll often see grounded white oak acorns with their first root already reaching for the soil.
In comparison to white oak acorns, burr oak acorns are big — robust, you could say. Some get to be more than 1½ inches long. But the cool thing about bur oak acorns is that the fringed caps. These cover about half of the nut, and it often looks as if a person pulled his hat down over his head with his hair sticking out underneath.
If you find a pair of acorns attached to a long stalk, you’ve got a swamp white oak. The cap covers about one-third of the nut, which is 1 to 1½ inch long.
By the bark
That’s all well and good — but what if it’s January and there aren’t any leaves on the tree? What if the tree doesn’t have acorns? Then how can you tell the difference between these oaks?
Here’s where bark I.D. comes in. Identifying bark can be tricky. There are lots of adjectives to describe bark, but one person’s “furrowed” is another person’s “fissured,” and one person’s “grayish” is another’s “silvery.”
The best way to learn a species by its bark is to look at several individuals of that species and create a composite picture in your mind.
If you have the chance to see white oak and bur oak next to each other, you’ll see the difference in bark right away. White oak is definitely light-colored (ashy gray) and somewhat flaky looking. Bur oak bark is dark and deeply furrowed, with a tough-guy look about it. Swamp white oak, less common than white or burr, has bark with deep, irregular furrows.
Location, location
Where oaks are growing and how they’re growing is as important as the finer points of morphology.
White oak likes well-drained soils in upland habitat. It can spread its limbs out wide if given room, but in a forest setting it will grow straight and tall. Bur oak is the classic edge-of-the-prairie tree. Its widespread canopy can extend 50 feet or more over an open field. Bur oak can also grow in both upland woods and lowland forests.
Swamp white oak is found in unique habitats called flatwoods, where there may be standing water for weeks at a time in the spring, or it may be dry as a bone at other times of the year. It can do well in a poorly-drained area underlain by clay. No matter what the habitat, white oaks have a gnarled look.
All these features give oaks a certain gestalt. From the time explorers Jacques Marquette and Louis Joliet described these “lofty and prodigious” trees in 1673, oaks have been part of our history and heritage.
May there always be places where, as traveler Colbee Benton said of Illinois in 1833, “The tall, scattering oaks with their rich, beautiful and comfortable shades, (add) the finish to this charming and lovely spot.” Indeed.
Ÿ Valerie Blaine is a naturalist with the Forest Preserve District of Kane County. You may reach her at blainevalerie@kaneforest.com.
About this series
In this three-part series, naturalist Valerie Blaine looks at the native oak trees found in Kane County. The natural history and ecology of oaks provides a background for learning to recognize these great trees. Youll learn some easy identification tips, and find out how you can be involved in the restoration of oak woodlands in the forest preserves of Kane County.
Part 1: The decline of oaks in the Chicago suburbs (July 29)
Part 2: Meet the white oak family
Next up: Red oaks in Kane County