Don’t know what it is other than looking like something possibly in the Asteraceae. Are the central leaves showing prickles starting? Being an annual doesn't mean they can be left. Their modus vivendi is to live fast and seed copiously. Don’t allow them to flower.

Probably Youngia japonica.

I have this weed as well. Best to pull before it flowers, if you don't want a lot more, since it has lots of fluffy seeds like a dandelion

on some level.. anything that spreads that fast is within one of the definitions of WEED ... even if it were a good plant.. you would probably consider pulling up a good amount of them anyway ...

ken

This is an ugly invasive weed.

http://nc-ipc.weebly.com/youngia-japonica-hawksbeard.html