These seedlings are all over my back garden in Northern Virginia and I haven't been able to make an identification in spite of looking through pages of "weed ID" requests in this forum and pictures on various websites. The closest match I've seen is pilea pumila (clearweed) but the stems don't look translucent, and I don't see the three parallel veins on mine.

I have been hand pulling them, and they come up very easily. I am mainly curious to know what it is. I don't recall seeing it before last year, and have been in this house almost 20 years. The area has full sun for most of the day.

Anyone recognize it? Thanks!