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Fall 2009

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

December 1, 2009

Acorns employ varied germination strategies

White oak acorns aren't waiting for spring. The lucky ones that landed on soft soil -- and were missed by squirrels -- have had a warm, wet season to germinate and sink their radicles into the earth. Freezing temperatures will pause the rooting, but spring warmth will resume the growth and coax out leafy shoots. After a year, a tap root can stretch as much as a foot underground.


Pin oak acorns are a study in patience. They develop on the twig for two growing seasons before dropping and require a winter's cold treatment to germinate. A thick, waxy coating allows the little acorns to stand for six months in cold water without suffering damage.


The white oak group of oaks have smooth, rounded leaf lobes. Acorns mature in six months; some are sweet and edible. Wood is generally whiter than red oak. Species include white oak, overcup oak and bur oak.

The red oak group of oaks sports leaves with bristle-tipped lobes. Acorns are very bitter; wood is generally redder than white oak. Species include pin oak, northern red oak and scarlet oak.

SOURCES: U.S. Forest Service; Illinois State Museum