Tree of the Month, March 2024

Shingle Oak Quercus imbricaria

by Martin (Mort) Schmidt for Simply Living

Many people assume that all oak leaves have conspicuous lobes, but some don’t. Shingle Oaks, which are native to Ohio, have leaves that look more like magnolia. But like all oaks, Shingle Oaks have acorns. Leaf shape is useful in tree identification, but trees are classified primarily on the basis of fruits and flowers. When Swedish botanist Carl Linnaeus established the plant classification scheme, he reasoned that because fruits and flowers are essential to a species’ continuation, they were of prime importance when figuring out their relations to other plants. Centuries later, we know that his logic was sound, because plants with the most similar fruits and flowers generally have the closest DNA matches. But most fruits and flowers are present only briefly, so we usually focus on leaves for identification.

All oaks have simple leaves, i.e., they’re attached individually to the tree. Compound leaves have more or less constant numbers of leaflets sharing a petiole (stem), which, on deciduous leaves, are only used for one year. A familiar plant with compound leaves is poison ivy, which has three leaflets which, together with the petiole, make a compound leaf. (Leaves of three, let it be!) Oak leaves are attached to twigs, and twigs are attached to branches in an alternate pattern, such that leaves are attached at different points. Opposite leaves and branches are attached at the same point, directly across from each other. Additionally, oak leaves are pinnately-veined (feather-like), in which a primary vein runs the length of the leaf, and secondary veins are attached to it at various points along its length. Palmately-veined (hand-like) leaves have several primary veins attached at one point on the stem.

Left – alternate versus opposite arrangement. Right – pinnate versus palmate veining. Drawings by Mort Schmidt.

Unlike Ohio’s other native oaks, Shingle Oaks leaves have no lobes. The leaves occasionally have small teeth, usually in the juvenile stage. Most Shingle Oak leaves lack teeth, and might be mistaken for Sawtooth Oak (Quercus acutissima), but Sawtooth Oak is native to Asia, and is normally found in landscaping, not forests. You can also distinguish Shingle from Sawtooth Oak by their acorns, discussed below. Another unlobed oak that can grow in Ohio is Willow Oak (Quercus phellos), but its leaves are much narrower, and it’s mostly limited to states south of Ohio. But even without leaves or acorns, you can usually recognize oaks by the presence of multiple terminal buds, that is, bud clusters at the tips of branches. Also, Shingle Oak leaves are persistent, and tend to remain on the tree in winter long after other trees have lost their leaves. 

Clockwise from upper left – Shingle Oak leaves, Sawtooth Oak leaves, Willow Oak leaves, Shingle Oak terminal buds. Photos by Mort Schmidt.

Shingle Oak flowers take the form of small, yellow-green catkins, unlike the showy flowers seen in Black Cherry, Black Locust, and many others. That’s because oaks are wind-pollinated, and don’t need highly visible flowers to attract pollinating insects. Shingle Oak fruits consist of acorns between half and three-quarters of an inch long. The caps cover half to two-thirds of the nut, and they lack the bristles seen on Sawtooth Oak. 

Oaks are split into two groups, white and red. Oaks in the White Oak group typically have rounded leaf tips, and oaks in the Red Oak group typically have pointed leaf tips. This trait is helpful for field recognition, but the critical difference between the groups is in the germination of their acorns. Acorns in the White Oak group send out roots soon after falling, while acorns in the Red Oak group remain on the ground over winter before sprouting. (Notice that “Red Oak” can mean either the species Northern Red Oak, Q. rubra, or any member of the Red Oak group. Similarly, “White Oak” can mean either the species White Oak, Q. alba, or any member of the White Oak group. I use “Red Oak” and “White Oak” for the species and “red oak” and “white oak” for the groups). Red oak acorns are high in tannic acid and are less palatable to wildlife than white oak acorns. To reduce the odds of being eaten, white oak acorns quickly anchor themselves and deplete their store of carbohydrates, while red oaks wait until the following year to sprout. 

Left to right – Shingle Oak flowers and leaves, Shingle Oak acorns, and Sawtooth Oak acorn. Photos by Mort Schmidt.

Shingle Oak bark is less recognizable than some red oaks, especially Northern Red Oak or Pin Oak, which have bark with long, smooth ridges approximately an inch wide. Shingle Oak bark is often more rough and scaly. Mature Shingle Oak trees typically have a broad, rounded crown. 

Examples of Shingle Oak bark. Upper photos display long, smooth ridges also seen in Northern Red Oak and Pin Oak, but others are less similar. Photos by Mort Schmidt. 

Quercus imbricaria typically reaches a height of 60 feet and a trunk diameter of 1.5 to 2 feet at maturity. Ohio’s Champion Shingle Oak, located in Hamilton County, has a height of 104 feet, a trunk diameter of 4.6 feet, and a crown width of 101 feet, according to Ohio Champion Tree database

Oak identification can be confusing because of their tendency to hybridize. According to Flora of North America, Shingle Oak reportedly hybridizes with several others native native to Ohio, including Scarlet Oak (Quercus coccinea), Pin Oak (Q. palustris), Northern Red Oak (Q. rubra), Shumard Oak (Q. shumardii), and Black Oak (Q. velutina) all of which are red oaks. The difference in reproductive cycles makes it difficult or impossible for white oaks and red oaks to hybridize between groups. 

ID SUMMARY: Alternate, simple, ovoid, shiny, pinnately-veined leaves with smooth or occasionally, slightly toothed edges. Leaves similar to Sawtooth Oak, but Sawtooth is rare in forests and has frilled acorn caps. Also resembles Willow Oak but Willow has much narrower leaves and is native to the southeastern states. 

Shingle Oak prefers well-drained, slightly acidic soil, and open sun. It tolerates urban conditions and is an under-appreciated landscape tree. Q. imbricaria is native to the midwestern U.S. Lucy Braun’s Woody Plants of Ohio indicates that Shingle Oak occurs in nearly every Ohio county, except the far northeast and several counties near the western border. 

Shingle Oak range map. Image from U.S. Geological Survey.

The Purdue University Extension for Forestry and Natural Resources lists Shingle Oak as a “generally poor species” among the red oaks. Because of Shingle Oak’s limited commercial value, little information is available on its hardness and density. Most of Ohio’s red oaks have a Janka hardness of approximately 1,200 lbf and a density of 0.70 g/cc, according to the Wood Database, compared to the median of my list of 73 Ohio trees of 1,075 lbf and 0.64 g/cc. Shingle Oak readily splits, making it ideal for shingles, but less so for lumber. Nevertheless, according to the Native American Ethnobotany Database, the Cherokee made considerable use of the wood to make furniture, mortars for grinding corn, baskets, woven chair seats, and fiber. They also wrapped dough in Shingle Oak leaves to make bread. Medicinally, the Cherokee employed Shingle Oak bark to treat: 

  • dysentery,
  • mouth sores,
  • chapped skin,
  • infections,
  • fevers,
  • indigestion,
  • asthma, and
  • urinary problems. 

Like other oaks, Q. imbricaria‘s high heat value and readiness to split make it excellent firewood. 

Acorns are an important food source for rodents, deer, birds, bears, and other animals. But like other red oaks, the acorns’ higher tannin level makes them less desirable than white oaks. Some white oak acorns were, and some still are, eaten by people, but the red oaks’ high acidity makes them too bitter for human consumption. 

Most or all of the Old World oaks are white oaks. Consequently, there is little or no mention of red oaks in European folklore or literature. Even the term “oak” is suspect in ancient texts, because just as “apple” often meant simply fruit, “oak” often just meant tree. 

Shingle oak is an odd and attractive member of the oak group, with its oval, unlobed leaves. Look for multiple terminal buds and acorns without frilled caps.  

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You can also listen to my talks on Ohio Broadleaf Tree Identification on YouTube, Part 1 and Part 2

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