Some sort of geranium. In PA, I'd suspect Geranium molle.

Thank You GardenGal48 and Raee! That has to be it-I appreciate both of you identifying my little seedling!

could it be Geranium pyrenaicum, that looks very similar, is from southern Europe and is annual

I have found this weed here in Germany and Switzerland as well and just was never too sure what it was

Looks like it could be Creeping Charlie - ?

No. It's definitely a Geranium. Could well be molle, which I get a lot, but there are other similar ones. Never had pyrenaicum as a weed here.

Have you not, Floral? Amazed!. Both the purple and white are all over my plot (along with other weedy cranebills - phaeum and nodosum, none of which I really mind that much (in fact I went to some lengths to acquire a white nodosum, as well as a rather nice picotee lilac with pale edges). Oh yes, palmatum and maderense are also inclined to appear in multiple plant pots, having exploded around the garden.

Hmmm. Have I been misidentifying it all these years?

I'm convinced it is Geranium molle, I think you- Floraluck2 are correct. I googled Geranium molle and found whatt looks exactly like my plant. I will update with photos for all to decide for themselves once it matures and flowers!

This little plant ID'd as "geranium molle aka Dove's-foot crane's-bill - grew all winter long even in the snow! It has pretty foliage so I didn't pull it out , so here it is four months later now in May.

Turns out I do have Geranium pyrenaicum on the allotment!

Much larger flowers than Sue's, which I'm now suggesting is G. carolinianum.