I grew up in East Texas in the 1950's and 1960's.  There were wildflowers there that were called "Niggerheads," much like these Echinacea:

I actually heard of this last summer when a Southern friend told me the name of the flowers I'd just planted in my little beach garden in Ptown. A TP commenter notes:

In a hunting context, it's an archaic term meaning "big, round, rock". I heard the term as a kid hunting in Arkansas. It's a way to give directions, I also noticed that my Wallace voting, extremely racist, grandfather didn't use the term when interacting with African-Americans hunting in 1984 or whatever.

There must be other definitions as well. Dish readers, take it away!