I'm not sure of the ID....kinda looks familiar, tho.

Here is a link that might be useful: Unknown weed

Looks to me like Marsh Marigold. I have some growing here and there in my yard and they make a beautiful early spring flower display. Leave them in and see if they bloom. As delicate as they look, they are actually quite hardy and vigorous, although I wouldn't say invasive. They will spread slowly, but I think if I wanted to get rid of them, it would be easy.

http://www.ct-botanical-society.org/galleries/calthapalu.html

it's called 'false celadine' 'marsh buttercup' around here... and it's pretty, but really, really invasive, designated a noxious weed around PA, and is threatening the native population of mandrake, and several of the rarer wet-footed wildflowers in the region.

in your lawn? that's a tough one, since the 'cures' are aggressively digging them up, then digging up the shoots...and smothering them under newsprint mulch, which would not work in a lawn.