Nature Profile


Bur Oak

Quercus Macrocarpa

“Monarch of the woodland is the Oak, of all trees most dear to us who live in northern lands.” Ernest Henry Wilson, Aristocrats of the Trees

Native primarily to the central Untied States from Texas north to the southeast corner of Saskatchewan, into Manitoba and east to Ohio, Pennsylvania and New York and scattered north and east to Maine and the maritime provinces of Canada. This is one of our hardiest, most adaptable and remarkable oaks. The acorns of Quercus macrocarpa have a fringed cap that gives rise to its common names, bur oak or mossycup oak. Being in the white oak group, these trees have relatively palatable acorns favored by squirrels, turkeys, wood ducks and white-tail deer. The size of the acorns noted on The Holden Arboretum specimens are from 5/8” to 1 ¼” in diameter, with the amount of fringe or “bur” on the cap also being variable.

A pioneer species of the “oak openings” at the edges of the prairies, trees in this habitat have thick bark on their trunks and corky protrusions on their twigs. These trees are remarkably adaptable, competing with grasses in a seasonally hot and dry environment such as limestone bluffs. Another habitat that is occupied by bur oak is the bottomlands where the trees are adapted to seasonally wet, heavy soils. Native Quercus macrocarpa can be found in nearby Mentor and Willoughby, but bur oak has not been noted in Holden’s natural areas. Natural hybrids can occur with other trees of the white oak group, for example putative hybrids with Quercus bicolor (swamp white oak) here in Lake County.

In the Myrtle S. Holden Wildflower Garden at the eastern edge of the prairie garden is a fine 20-year-old bur oak, 36’ tall by 28’ wide, with corky branches that was grown from an acorn collected in Portage County, Ohio. It was planted on Sept. 14 1993 by the rotting stump of a Magnolia acuminata, which died during the 1988 drought. The idea was for the bur oak roots to follow the path of least resistance out into the surrounding heavy soil using the paths made by the decadent roots of the cucumber magnolia. This resulted in an average growth rate of about 21” per year, in contrast to the average rate of about 12” per year of 10 other bur oaks measured at Holden.

Another fine specimen from the same accession – sister acorn of the above  planted in the Theodora Owens Pennington Bed on the south side of the Wildflower Garden – had an abundant crop of large acorns in 2007 at the age of 19 and has grown 34’ x 26’. On the northeast side of the Warren H. Corning Visitor Center parking lot is a bur oak without corky branches that was planted as a balled and burlapped 3 ½” caliper specimen in November 1979, which now measures 52’ x 36’. Our most venerable specimens were planted at Lantern Court along the west side of the entrance drive in the early 1930s and is now 64’ x 53’; and in the Helen S. Layer Rhododendron Garden by the path to Beech Knoll across from Oak Pond, a specimen probably planted in the early 1940s  is 70’ x 58’.

The bark of mature trees is light ashy gray and deeply furrowed. Branches and foliage are fairly coarse. Foliage unfolds in May and the yellowish-green drooping male catkins shed their pollen shortly after leaf emergence. Leaves are distinctively lobed, being glossy dark green above with paler tomentose undersides. Leaves turn a rusty yellow or yellowish-brown before falling in early November along with the acorns. Quercus macrocarpa ‘Ashworth’, north of Oak Pond in the Layer Rhododendron Garden, drops its acorns and leaves in mid to late October.

During some wet years the foliage can be disfigured by anthracnose and various insects may feed on the leaves. Bur oak is resistant to pollution, salt, heat and drought. Despite being taprooted and therefore relatively difficult to transplant, the only bur oak tree that died here was planted in the middle of an old road bed in shallow soil. Given that these trees can live for 400 years, we look forward to enjoying them for generations to come.

Photo credit: Bruce Kirchoff from Greensboro, NC, USA, CC BY 2.0 , via Wikimedia Commons

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