I have a few score of these plants underneath my weeping cherry. The general habit is pachysandra-like (fleshy stems running along the ground), but I don't think it is pachysandra. The leaves sprout out all around the stem, radially. At the end of each stem is a rosette with 5 small nodules inside. The leaves are green on top and purplish red underneath. The stems also have this purplish hue.

My soil is acid, and the spot gets full morning sun. The area they are growing in is covered in pea gravel and the plants have erupted through it. I am in zone 6b in central NJ.

Any idea what this is? The previous owners planted a formal japanese garden in this spot, so this could be some sort of intentional planting run amok, but the plants are straggly and ugly and weedy to me.

Thank you!