Among with such symbols as U.S. national mammal and bird, there are different things adopted as the symbols of the U.S. states. Some states have official state fruit, animals, vegetables and so on. Such symbols as flowers are also quite popular. The flower symbol of the state of Ohio is the Scarlet Carnation.

Although the fruit of the buckeye tree has symbolized Ohio since the mid 1800's it wasn't until 1904 that the Scarlet Carnation was chosen as Ohio's official state flower. The flower was a favorite of William McKinley, former U.S President. And the flower was adopted by the state legislature partly because it represents a token of love and reverence for the Ohio's William McKinley.

More Info: en.wikipedia.org