What're these?

[Beth_B]

For me, the leaves look more like Artemisia vulgaris ( 'Limelight'), which is sold here. It looks like a young plant between which an Anemones grows.
I did not see exactly such an Anemones. But I saw plants of this family with mottled leaves. For example,
Ranunculus repens variegatum or certain class Anemonella.
In any case, it will be interesting to know.

Oh wow, certainly looks exactly like the Limelight! But now I'm so confused about those flowers. I swear there was only those two in the clump I pulled up... of course I've been wrong before.

Just checked, only those two plants in that patch, and no sign of buds. Darn, those were pretty flowers. If it was something else coming up from underneath, it didn't make it through the winter. Whatever it was, was flowering by late May.

 

[Owdboggy]

The Artemisia is classed as a thug. It will spread indiscriminately and is very difficult to get rid of, so be warned.

 

[Beth_B]

It's certainly exploded in size since I planted it last year! Luckily there's nowhere it can go far. It's on a small strip between my driveway and the fenced yard. Can't go into the driveway, and anything on the other side of the fence gets regularly mowed and weed whacked.b