Photo of the Day: Build Me Up, Buttercup

My dad calls these flowers (now blooming) "buttercups," though he says he's not sure if that's the proper name for them.

If there are any green thumbs out there, I'd appreciate it if you could let me know what these are generally called (even though I've already taken a liking to the one my dad uses for them now, and am reluctant to part with it).