A typical google result...
Brussels sprouts—the variety of cabbage with a stout stem and a budlike head of tightly folded leaves—are named after the city of Brussels. The modern version of the plant was originally grown primarily in the area of Northern Europe now known as Belgium, of which Brussels is the capital. In the name of the cabbage, Brussels is usually capitalized like the name of the city, though some publications don’t capitalize it.
The Wikipedia page doesn't even say "Brussel sprout" is an error. It avoids the term entirely.
That sounds naughty.