In 2007, Oklahoma made watermelon its official state vegetable.
Yes, you read that right: on April 17, 2007, the Oklahoma State Senate passed a bill declaring that not only is watermelon a vegetable (related to cucumbers, they said), it's also the state's official vegetable. (Source)
Other states have official vegetables are:
Arkansas - South Arkansas vine ripe tomato
Georgia - Vidalia sweet onion
Idaho - potato (what else?)
Louisiana - sweet potato
New Mexico - chile and pinto bean
North Carolina - sweet potato
Texas - sweet onion
Utah - Spanish sweet onion
Washington - Walla Walla sweet onion
we really need to educate our leaders