Don't know but could it be a Portulaca sp. of some type?

FataMorgana

I don't think so. The soil and air has been way too cold for that. We've had freezing temps at night. Portulaca would burst.

I think that foliage is all connected, not separate.

Sedum reflexum?

looks like sedum acre. Mine is just coming up, and looks exactly like that.

I asked the head of a herbarium at a university. He told me I would need to see the flowers , that juvenile foliage is problematic to ID.
I have not noticed other Sedum in the area.

It's a sedum. Probably one of the 'acre' varieties. When you see what the bloom color is, you can identify that.
Could have been a hitchhiker in a potted plant or seeds
passed on by birds or the wind.
Pam

There are several native sedums in North America, one of them being sedum glaucophyllum (see below), but the chances are greatest that it is a hybrid cultivar or other non-native.

Here is a link that might be useful: sedum glaucophyllum