Now renamed Ficaria verna, I believe, aka Lesser Celandine.

Thanks so much for identifying it. That is it, Chelidonium majus. It may or may not be floro pleno, as I think my flowers are a bit small. But definitely that species. Not sure where it came from, but I like it and will let some of the pods dry out and will plant the seeds. This is a great forum!

Maybe a Silphium? They're native wildflowers you might see in a garden center in Illinois. Prarie Dock, Silphium terebinthinaceum, has big basal leaves. WW Here is a link that might be useful: Prarie Dock

I wonder if it will give me its usual purple flower as well. These scapes are definitely attached to the plant.There don't seem to be any other scapes in amongst the leaves. 100% sure it's not coming from another plant/bulb underneath. This is a very small raised planter about 3' long x18" deep, only 2 bricks high, and I filled it with old potting soil and compost. Do any other hostas do this?