From Ohio History Central
In 1953, the Ohio legislature designated the Aesculus glabra, or the Ohio Buckeye tree, as Ohio's official state tree. The tree is called the buckeye tree because its nuts resemble the shape and color of a deer's eye. The buckeye tree is relatively common to Ohio, growing especially well along rivers and streams and in floodplains.
People commonly confuse the buckeye tree with the Aesculus Hippocastanum, or the horse chestnut tree. In addition, the Aesculus octandra, or the yellow buckeye tree, also grows in Ohio. It is closely related to the Ohio Buckeye tree, and it is difficult to differentiate between the two species.
The buckeye tree has also provided Ohioans with their principal nickname, Buckeyes. The Ohio State University has adopted Brutus Buckeye as its mascot. Ohioans have referred to themselves as Buckeyes since at least the presidential election of 1840, when Ohio resident William Henry Harrison won the presidency. Harrison's supporters carved campaign souvenirs out of buckeye wood to illustrate their support for their fellow Ohioan.