SOLVED! Thanks growin - I googled for some images it is certainly a yarrow! I've just never seen it flowering.
This little plant is growing next to my porch on the ground in Massachusetts. The pencil is in the photo for scale - it is a small plant. I would like to take some indoors to make a houseplant. I just need to find out what it is in order to decide if that is a good idea. Thanks.
Well, if it is a yarrow, it's not "any species" of yarrow, needless to say - it would be a particular species of yarrow and I was wondering which you and growin thought it was.
A close-up photo would help.