The Bur Oak
Nature Bulletin No. 708 March 9, 1963
Forest Preserve District of Cook County
Seymour Simon. President
Roberts Mann, Conservation Editor
THE BUR OAK
The state tree of Illinois is the "native oak". It should be the Bur Oak.
As Aldo Leopold discerned: "When school children vote on a state
bird, flower, or tree, they are not making a decision; they are merely
ratifying history". Ergo, when the first settlers gazed westward across
the vast prairies of Illinois, bur oaks were the burly trees on knolls and
ridges which stood like ships in a sea of grass.
Those oak openings, as they are called, were remarkable features of the
tall grass prairies in Indiana, Illinois, and the prairie peninsulas that
extended northward into Michigan and Wisconsin. Many early travelers
wrote lyrical descriptions of those park-like openings "without a twig of
underbrush". . . "where deer grazed leisurely like sheep"...."so open that
a cabriolet could have been driven through them for miles".
They existed because a bur oak is the only tree that can be swept by a
roaring prairie fire and still live. It is insulated, even on the twigs, by a
crust of corky bark. On the trunk of a huge patriarch its deeply furrowed
bark may be four inches thick. On a sapling the stem, branches and
twigs are covered with weird assortments of corky ridges and
Although most numerous in the Middle West, the bur oak is distributed
from Nova Scotia to Manitoba and south to Delaware, Tennessee and
Central Texas. In Illinois it grows throughout the state -- probably in all
of the 102 counties originally. Here in Cook county, and as a rule, it is
most common on deep rich soils that are moist but well-drained.
However, the species is surprisingly adaptable. It frequently flourishes
on gravelly moraines and sandy ridges underlain by water bearing strata
and some of the largest bur oaks in Illinois -- giants more than 350
years old and 5 or 6 feet in diameter -- grew on such soils. On the other
hand, in LaSalle and adjacent counties, bur oaks are found on dry
uplands in company with hickories and white, red and black oaks.
This tree is one of the largest and, next to the white oak, most majestic
of American oaks. Its stiff gnarled branches and stout, frequently
crooked, branchlets with corky wings along them are distinctive.
Ordinarily, it is seldom more than 80 feet high and 3 feet in diameter
but, in favorable locations such as the Wabash river basin, giants 170
feet tall and 7 feet in diameter have been known. a forest it develops a
tall clear trunk but, growing in the open, we have seen some with short
massive trunks, huge lower branches almost horizontal, and a spread of
80 feet or more.
Its leaves, largest of all the oak leaves, are from 6 to 12 inches long, 3
to 6 inches broad in the upper portion, with from 5 to 7 lobes which,
since it is a member of the white oak group, are rounded. The central
lobes are separated by wide bays or sinuses that reach almost to the
midrib. Those thick leaves are dark green above but silvery green and
downy underneath. In autumn they become dull yellow or tan and,
unlike other oaks, all drop off.
The Latin name for all oaks is Quercus. The scientific name for the bur
oak is Quercus macrocarpa, meaning large-fruited. The common names
-- bur or mossy cup -- refer to its distinctive acorn. Egg-shaped and
from 3/4 to 2 inches long, it is held in a deep scaly cup which has a
fringe of elongated scales and sometimes covers more than half of the
acorn. Its white kernel is sweet and edible.
The wood -- hard, strong, tough and close-grained -- is almost as heavy
as white oak and equally valuable for many purposes such as lumber,
veneers, furniture, interior trim and flooring. Because of its durability in
contact with the soil, bur oak is frequently used for piling, railroad ties
and structural material.
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Update: June 2012