Tree Notes is about trees -- especially native trees, trees for wildlife, and trees in history.

Thursday, October 8, 2009

Bur oak: America's largest acorn

Mossy cup oak acorns

It's tree trivia time! Did you know that the acorn of the bur oak (Quercus macrocarpa) is North America's largest native oak acorn? A very large bur oak acorn might measure up to 2 inches in length.  Most bur oak acorns are in the range of 1 inch to 1-1/2 inches in length.

The bur oak is sometimes called  mossy cup oak, a name that refers to the fringe around the edge of the acorn cup. Usually, the cup covers about half of the nut, but occasionally, the cup will be so large that only the tip of the nut sticks out of the fringe. Another common name for the bur oak is overcup oak.

The twigs of bur oaks have corky ridges. If you click the photo above and enlarge it, you can see ridges on both sides of the twig, giving it an irregular, thickened outline.

The acorn in the photo is growing on a bur oak that my husband planted. In the fall, he gathered fallen acorns from the big bur oaks at his childhood home in Independence, Missouri. When he got back to Kentucky, he planted the acorns in clumps of half a dozen, a few inches deep. He wasn't particularly fussy or scientific about it. A number of little oak trees came up the next spring, and he thinned them down to this one.

This tree, and several other bur oaks he planted at the same time are now about 15 years old. At 25-30 feet, they are big enough that they are becoming significant trees in our landscape. They grew slowly at first because they were establishing their roots, but now they seem to be growing two  feet or more annually. They have been bearing acorns for several years.

The bur oak, a member of the white oak family, is native to much of the eastern United States and part of eastern Canada.  It commonly lives for several centuries and individuals trees in favorable conditions may live much longer. In maturity, it may reach 100 feet in height and in spread. Many creatures of the wild enjoy its acorns and some nibble the twigs as well.

20 comments -- please add yours:

new york city garden said...

As a child, I lionized maples because of their fall color. Oaks were just the backdrop to landscape maples. As an adult, I've come to love the oaks that I grew up with and the huge variety of them is amazing.


Genevieve said...

I am only familiar with the oaks of the eastern U.S., but there are also some species of oaks that are native only to the western U.S. Around a dozen of these western/southwestern oaks are live oaks (evergreens).

Eastcoastdweller said...

A few years ago, I donated a burr oak that I had nurtured from acornhood, literally, to a local college campus. I had carried the seedling with me from college.

Last year, they ripped it out of the ground to make way for a temporary construction access road that could easily have been put somewhere else.

I will never donate a tree to a college again.

That burr oak had been on its way to becoming a grand specimen, as well as a rarity here in Virginia.

Genevieve said...

I, too, would find that hard to forgive and forget.

KaHolly said...

I googled the fringe acorn so I could label it in my picture file and came across this wonderful post! I found a bur oak tree in Central Maine. Thank you so much for all the information! ~karen

Galsher said...

Live and wonder!
My daughter Katya walked with her friend another day, and brought one acorn to me. I was amazed by its size and run to meet the mighty oak, producing such miracles, and collect a few more.
Please see the photographs at
More than 6 (six!) inches of measuring tape is required to wrap around such an acorn. What a giant!
I’ve heard that “everything is big in Texas”… well, these acorns are growing in the right place.

Col. Ron said...

Is there a red oak similar to the bur oak? I recently found a small red oak that had enormous acorns. The acorns are like the bur oak acorn, but not a hairy. This was in Jasper County, Texas on the Neches River. I grew up in this area and I thought I knew every tree in East Texas, but I had never seen this one before.

Ron Strybos
Kountze, TX

liz granbury tx said...

Although the Burr Oak is evidently not native to the North Central Texas or Texas Hill Country, I just discovered a larged grouping alive and well in a mall parking lot. They are thriving and producing lovely large acorns. Can't wait to harvest some and see if they will eventually germinate.

Anonymous said...

We have Bur Oak planted and growing in Katy, Texas

Anonymous said...

I live in Hendersonville TN by Old Hickory Lake. I have found a Burr Oak that has huge acorns, but unfortunately all I can find are the cups. The largest that I collected has an inside diameter of 1.5 inches. So my guess is that the acorn itself must have been at least 2 inches. Next year I will visit the tree in early September and see if I can get a full acorn before the deer eat them all.

Anonymous said...

Grandbury, the bur is native to many places in north Texas and down into central Texas . Some are quite large in the wild.

Anonymous said...

If ever in Dallas, go to Presbyterian Hospital on Walnut Hill/Greenville Ave....the largest acorns collected in Oct/Nov. Bur oak acorns are 2"-4" wide! I gathered about 20 and "water tested" all, salvaging 15 acorns, planted them & shared the harvest, a 2' + beautiful harvest in May with family & friends.

Rockwall's Lake Pointe Hospital grows the best Shumard Red Oak acorns; both North Texas grown trees and yes, I do roam collecting the fruits given by nature. ;)

Anonymous said...

I live in the high desert 70 miles from Las Vegas and I planted a Burr oak about 10 years ago. It is now shading my courtyard. I looked it up because I found an odd acorn under it this year, only one ever. It's a lovely tree that is the 1st to lose it's leaves in fall and last to get them in spring out here.

Anonymous said...

My father gave me a seedling from a tree he had sprouted from a Bur Oak acorn. I live in Columbia, Tn, and the tree is now 20' tall, but has never had acorns. Are they self pollinating, or am I going to have to provide another tree?

Malak Macabre said...

I picked up some from a tree in Abilene, TX and I had no idea what they were. I want to plant a couple of them as a part of my legacy. (Ha ha)

Anonymous said...

I'm in Texas, NORTH west Houston area and just found these trees and acrons. Amazed!!!

Anonymous said...

I was picking up pecan's in Landa park, New Braunfels Texas this last weekend and my daughters brought me some of these acorns. I didn't think they were acorns, but now I have to tell my girls they were right and I was wrong... They always love that!
Thanks for your site!

Mark J. said...

I live in Buffalo Gap, Texas and I'm researching the Burr Oak. I'm planting the acorns this winter to grow for the local deer on my land and for hunting. I'm curious about the taste, whether it's a sweet or bitter acorn. Although, my dad who lives in Cisco, Texas says that deer love the acorn.

Unknown said...

I just discovered this tree in downtown Manhattan. It's in Battery Park City. My son and I watched the squirrels stuff their face with the giant acorns.

Sidney Matheney said...

I planted a Bur Oak on a pot a few weeks ago and now there is a one inch tall tree growing. I plan to transplant it this spring, 2016.
My wife removed the shell and it germinated about two or three weeks later.

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"The power to recognize trees at a glance without examining their leaves or flowers or fruit as they are seen, for example, from the car-window during a railroad journey, can only be acquired by studying them as they grow under all possible conditions over wide areas of territory. Such an attainment may not have much practical value, but once acquired it gives to the possessor a good deal of pleasure which is denied to less fortunate travelers."

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Print references I frequently consult

Benvie, Sam. Encyclopedia of North American Trees. Buffalo, NY: Firefly, 2000.

Brockman, C. Frank. Trees of North America: A Guide to Field Identification. Ed. Herbert S. Zim. New York: Golden, 1986.

Cliburn, Jerry, and Ginny Clomps. A Key to Missouri Trees in Winter: An Identification Guide. Conservation Commission of the State of Missouri, 1980.

Collingwood, G. H., Warren David Brush, and Devereux Butcher. Knowing Your Trees. Washington: American Forestry Association, 1978.

Dirr, Michael. Dirr's Hardy Trees and Shrubs: an Illustrated Encyclopedia. Portland, Or.: Timber, 1997.

Elias, Thomas S. The Complete Trees of North America; Field Guide and Natural History. New York: Book Division, Times Mirror Magazines, 1980.

Grimm, William Carey. The Book of Trees;. Harrisburg, PA: Stackpole, 1962.

Hightshoe, Gary L. Native Trees, Shrubs, and Vines for Urban and Rural America: a Planting Design Manual for Environmental Designers. New York: Van Nostrand Reinhold, 1988.

Little, Elbert L. National Audubon Society Field Guide to North American Trees. New York: Chanticleer, 1996.

Martin, Alexander C., Herbert S. Zim, and Arnold L. Nelson. American Wildlife and Plants. New York: McGraw Hill, 1951.

Mitchell, Alan F., and David More. The Trees of North America. New York, NY: Facts On File Publications, 1987.

Randall, Charles E. Enjoying Our Trees. Washington: American Forestry Association, 1969.

Settergren, Carl D., and R. E. McDermott. Trees of Missouri. Columbia: University Extension, 1995.

Sternberg, Guy, and James W. Wilson. Native Trees for North American Landscapes: from the Atlantic to the Rockies. Portland: Timber, 2004.

Wharton, Mary E., and Roger W. Barbour. Trees and Shrubs of Kentucky. Lexington: University of Kentucky, 1973.

Wyman, Donald. Trees for American Gardens. New York: Macmillan, 1965.

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