That is a spotted spurge. Give it no quarter, hoe it and do not compost it, bag it, then place it in the trash. Each plant has umpteen billion seeds, (well probably in the thousands not billions). University of California has a pest management page just for Spotted Spurge, read it and go to battle. If possible, remove it before it goes to seed.
May your landscape soon be void of spotted spurge!
Thanks. Now a follow up question:
I fight this stuff all the time, and new growth never gets to be more than a few inches in size, then is hit with Roundup. I can’t understand how new sprouts get started. They even appear in the tiny cracks between pavers in our patio - in areas where there is no water from irrigation.
They have a ton of seeds so there is a large seed bank just waiting to spring into action. Persistence is the key. Keep after them, and encourage your neighbors to do likewise.e