Bur Oak: largest native acorns

In Texas the acorns may be the size of golf balls!

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Looking up through the bur oak

While the spelling of bur oak is sometimes burr oak, according to Sibley* it is also called a mossy-cup oak or blue oak. The Lady Bird Johnson Wildlife Center adds more names to this list, including Savanna oak, overcup oak, prairie oak, mossy-overcup oak. To add to the confusion, in certain terrains it can be referred to as scrub oak.  It would appear some of its names are related to the various habitats in which this species, Quercus macrocarpa, grows. Alternatively, it refers to the appearance of its acorns.

This white oak is native to much of the eastern and midwestern United States and Canada, although its characteristics vary depending on its location. According to Iowa State University, this tree has the most variable characteristics of any of the oaks. For example, its acorns are large in its southernmost growth area while they can be about a fifth the size in the northern regions.

The overall height of the tree also varies by its habitat. In northern climates it may only grow to half the size of the same species in southern latitudes.  This year saw a new national champion bur oak be honored in West Virginia. This specimen is a bit over 107 feet tall and has a trunk circumference of more than 278 inches. Models of climate change have predicted  bur oak may have an increase in its range, but the locations where it thrives may also shift. Due to its long taproot it may be able to withstand drought conditions.OLYMPUS DIGITAL CAMERA

Its acorns can be the largest of the native oak species and are well fringed, hence its mossy-cup moniker. Its Latin name is related to the acorns; marco means large in Greek and carpa refers to fruit. One author states burr oak acorns in Texas are golf-ball sized! Iowas State University allows the trees do not bear fruit until they are 35 years old. Most sources state the trees can live 300 to 400 years. The university site also states the lumber of the tree can be used like white oak, but isn’t as valuable due to its many branches. The USDA mentions  the most valuable bur oak trees for lumber come from Iowa and Illinois where it is usually marketed generically as white oak.

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Bark of the bur oak

The trees provide food to 96 or more species of wildlife, including black bears. According to this article, acorns are the primary high quality food source for black bears in northeastern Minnesota. Cattle and other livestock may ingest seedlings and acorns even though this material may prove poisonous in large quantities. This same source specifically mentions the Cheyenne of Montana as having eaten a mixture of acorns and buffalo fat.

Like other trees in general, and other oaks in particular, parts of the bur oak have been used medicinally. A unique mention is made of tree galls used to treat intestinal problems and as an antiseptic.

The tagged Quercus macrocarpa in Fort Collins City Park was planted in 1979. It is located between the reservable shelter and the road to the golf course. Look for the electrical box painted with a black cat. If you point to the east at a diagonal from the box, you should be in line with the tree. OLYMPUS DIGITAL CAMERA

  • Sibley, David Allen. The Sibley Guide to Trees, 2009.

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