Bur Oak: An Uncommon Source of Acorns in the East
Oaks are generally divided into two major groups: red oaks and white oaks. Red oaks have bristle-tipped leaves, acorns with hairy shell linings and bitter seeds that mature in two seasons. White oaks have leaves lacking bristles on the lobes, acorns with a smooth inner surface that are sweet or slightly bitter and mature in one season.
Bur Oak (Quercus macrocarpa). also called Mossycup Oak, is in the white oak group and is easily identified by the corky ridges on its young branches, deeply furrowed bark and acorns with knobby-scaled caps (cupules) with a fringed edge. This member of the beech family (Fagaceae) derived its common name from the resemblance of its heavily fringed caps to the burs on a Chestnut tree, though the caps only half cover the nut. Common in central U.S., Bur Oak is relatively uncommon in New England, occurring in in central Maine, New Hampshire, the western edges of Massachusetts and Connecticut, and the Champlain Valley in Vermont.
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Oak Leaf Shapes & Sizes
There are roughly 90 species of oak trees in North America, several of which can be found in New England. (Eastern White, Northern Red, Eastern Black, Burr, Common Chinkapin, Swamp White, Pin, Chestnut, Bear, Scarlet and Common Post). When identifying oaks, several characteristics, such as buds, bark, branching pattern and leaves, can be used. Most Northeastern species of oak have lobed leaves, with the lobes deep or shallow, pointed or rounded.
One thing all oak leaves have in common is their variability. Even on a single tree, you can find leaves of widely differing shapes. One reason for this is that the amount of sunlight that reaches them affects their shape. Leaves that are shaded are not only often larger than those that are bathed in sunshine, but their lobes are far more shallow. Both of these traits maximize the intake of sunlight. Canopies of oaks have a larger proportion of small, deeply-lobed leaves than lower down on the trees, where you can often find relatively large leaves that appear to lack lobes completely. The two pictured leaves come from the same Northern Red Oak. Can you tell where on the tree they probably grew? (Thanks to Penny March for post idea and leaves.)
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