Not any kind of Ranunculus. I've never seen poison oak but that's what it looks like to me.

Agree that it resembles poison oak, but I believe it is broadleaf toothwort (Cardamine diphylla)

IMHO, Cardamine diphylla seems to have much more serrated edges (these are rounded more like poison oak) and I would think at this time of year there would be flowers present to confirm it and C. diphylla doesn't seem to have the whitish leaf veins or the leathery look, but that's just a non-expert opinion. But I guess if davidrt28 handled the leaves he may already have his answer.

Scary! I have NEVER seen a Toxicodendron on the east coast that looks like this...but I suppose it could be.

Getting hit with herbicide now for sure.

The Cardamine has different texture leaves.

One of the things that is a mystery though, is regular old Toxicodendron radicans grows like gangbusters around here. If I'd left one in the ground from last spring, when I first noticed this, it would be at least 10' now. This has pretty much just sat here like this, slowly sizing up. So, either this is something else, or the obviously rarer Toxicodendron pubescens is much slower growing?

I had never touched it, obviously, or I would know for sure!

I just wanted to make sure it wasn't something potential rare and/or desirable. The Cardamine is ornamentally underwhelming and not particularly rare, so I won't mind killing it if that's what it is.

Maybe it is just plain old Toxicodendron radicans. Here in SW MI it can be extremely variable and even look similar to poison oak. Early spring leaves can even have that leathery/waxy look to them. However, those white/lite colored leaf veins and the very blunt/rounded leaf tips are unusual, the closest thing I have saved is in these photos.

According to the USDA "Atlantic" poison oak (Toxicodendron pubescens) isn't found in MI:

https://plants.usda.gov/home/plantProfile?symbol=TOPU2

Of course that doesn't mean that it is totally impossible to find it outside of the map seen there.

The fact it has stayed acaulescent for so long, makes me think it's a herbaceous perennial after all. https://www.plantdelights.com/products/dentaria-diphylla-american-sweetheart

I'm going to wait a little longer. If it produces poison ivy flowers I will zap it.

ALSO, forgot another obvious clue. It's in leaf in winter, and partly dies back in summer. Any Rhus relative would do the opposite.

Eastern Poison Oak, Toxicodendron pubescens can have both rounded or sharp cut leaflet lobes. The terminal petiolule is much longer, and the leaves and stems are puberulant giving it a felty appearance.

Toxicodendron pubescens.

Toxicodendron pubescens.

I knew the petiole didn't look right from the start, but thought maybe it was a Rhus, because it also resembles Rhus aromatica Lol. Brassicaceae didn't jump into my mind. Looks like it could be something in Vitaceae also. Cardamine has such a wide diversity of leaf shapes and variations. The local species hirsuta and concatennata are instantly recognizable, but I've never encountered diphylla.