Leaf is about the size of a thumbnail. I've never seen it flower. Confirmation it is some kind of Oxalis is sufficient. Thank you very much.

Agree.

Hard to control; dig when you can. Don’t rule out full strength Roundup concentrate. I apply with a small paintbrush.

Good luck.

Thank you, Iochroma.

If it's anything like the one I have here, you have to be careful to get the tiny bulblets that form around that central root just under the soil. Mine are the size and shape of a grain of buckwheat, and break off at the slightest touch, which of course allows them to spread like crazy. I dig a clump of soil up with the plant so I don't leave all those 'seeds' in the soil.

The photo looks like there may have been bulblets attached to the stem, but they're gone.

I couldn't find a photo online, but found this illustration that looks like mine, showing the clusters of bulblets - I think mine is oxalis violacea

Yes, it is as you say. I cannot shake the soil off or seeds will break away. I think I have two types of Oxalis plus Bur Clover in my lawn. Thank you for your comment.

I don't mind them in the lawn - since mine is a mix of many different groundcovers, but in my veggie beds is a totally different thing. I had to basically scrape off the top couple inches of soil to get rid of them - and I still missed some of those bulblets, which are now starting to sprout - grrr 😡