Consider Apiaceae, such as Thaspium trifoliatum, and Brassica.

Was it growing in sun or shade?

^ More in the shade...like the understory.

>To me it could be Asteraceae<

I'm thinking sunflower family also. On the face of it that narrows it down to tens of thousands of species. But maybe you can filter for this one looking at accounts of local weeds or wildflowers.

Of course, you may need the flower heads to be sure.

Ok, here's some more pics a year later:

Maybe Woodland Lettuce (Lactuca floridana), or something else?

And with some flowers now:

Well, that's was Asteraceae and I bet it has white sap. A Lactuca looks very likely. I have no idea which ones would occur in your area.