Strange leaves in my back yard.

I found these in my back yard next to the house today, and can't seem to find anything like them online!  They look nice, but they seem to grow very quickly because they haven't been there long.  I thought for a while that they might be the Mile a Minute Weed, but the leaves are backwards for them to be that.  There are three leaves, all connected to the stem at the acute angle of the triangle.  Any ideas?