Not sure, but they're vigorous! I have one little farm where they're thick, but it's been overgrazed more years than not. I just have two horses, a welsh pony, and a donkey on it now. Less buttercup this year than most. It's a pretty easy kill for me really, 2,4d or crossbow early does the trick.
Wild buttercup here doesn't discriminate no matter how fertile your pasture..gotta be sprayed fairly regular..two things it loves is,wet and cold..you can knock it back ,but it ain't going away completely ..