Ranunculus ficaria.

Thank you! That is what it is and what a relief to know that once it blooms it will disappear and I don't have to worry about how aggressive or invasive it is!

Oh, oh. No, it won't disappear. It's a perennial. And it has *numerous* small tubers at the base of each & every plant.

About the only chance you have to stop is where it's "beginning* to invade. My condolences. This is now your new hobby.

It disappeared last spring after it finished blooming?

I've read that it is extremely invasive, but with such a short life cycle and it dying back in April. I don't see it being much of a problem for me. I have a floodplain forest area that is carpeted with the stuff in the early spring, but then the forest is taken over for the rest of the season by garlic-mustard and stinging nettles, so I'll take the fig buttercup over them anyday!