The legal case here is Nix v. Hedden, 149 U.S. 304 (1893) (yay citations) and went all the way to the Supreme Court. The story behind it is this: in 1883, the Tarriff Act imposed a 10% duty on all imported vegetables, but none on fruit. Seeing a good chance to increase collections, the New York Customs Collector declared the tomato to be a vegetable, and incensed importers sued.

The case made its way to the Supreme Court, where the historical proclamation was made by Justice Gray that:

“although botanists consider the tomato a fruit, tomatoes are eaten as a principal part of a meal, like squash or peas, (and all grow on vines), so it is the court’s decision that the tomato is a vegetable.”

This decision legally defined a tomato as a vegetable in the United States and imposed the same tarriffs as for vegetables on them, casting aside hundreds of years of scientific knowledge like so many votes for Al Gore.