Euphorbia maculata - spotted spurge.

An annual.

A bazillion seeds per plant. (And your plants already have them.

Easy to pull up -- has central root -- do it a soon as you see them. Or cut off younger plants ( seedlings) with a scuffle hoe.

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Thank you! And yes, I had noticed that it comes from a central root and pulls up very easily. Luckily, I typically catch them fairly early and pull them up. I just happened to walk past this prime example at work when I realized I'd never found out what it was. I figured I'd take a picture and post here for info.

Thanks again for the help.