Acorns are the fruit of oak trees, but not all acorns look alike. Acorns differ in color, size and texture depending on the type of oak from which they are produced. A nut resembling what you commonly think of as an acorn, most likely is a different type of acorn. The cap-like structure on the upper part of an acorn is the cupule. That plus the nut make up the acorn. Oak trees produce acorns during autumn; one tree can produce thousands of acorns. Oak trees can live up to 200 years or longer.
The live oak is a massive shade tree with evergreen foliage. This species grows from southeastern Virginia to southern Florida and Texas. The acorns are ¾ to 1 inch long and rounded with a pointed tip. Acorns on live oaks are light brown within the cap that covers ¼ of the dark nut. The largest part of the acorn is dark brown to black and shiny. The acorns occur either by themselves or in clusters of three to five nuts.
There are several species of red oak. These hearty trees grow from Canada into the eastern and midwestern United States. Acorns on the Southern red oak are only 1⁄2 inch in diameter and have a thin, shallow cup, while the acorn on the Northern red oak is 1 inch long and oblong in shape.
The white oak is widespread across eastern North America. Acorns on the various species of white oaks range from 1/2 to 3/4 of an inch long. The Burr oak has the largest acorns of all North American oaks, measuring 1 1/2 inch in diameter. The cupule is scaly and has a hairy fringe at the rim.
The pin oak is distributed from the middle Atlantic states westward, to the edge of the Great Plains. Pin oaks grow faster than other oak species. Their acorns are rounded, about 1⁄2 inch in diameter and often striped with many dark lines. They have a thin, saucer-shaped cupule.