I think I know what this is. It looks like Euphorbia lathyris, more commonly known as Gopher Spurge.
It's not a very attractive plant and it will spread, but wear gloves if you plan to pull it out. Some people get a nasty rash from handling it.
It's sold in nurseries here as a gopher repellant, but it isn't. It just isn't very tasty to them, so they eat everything else and leave it for last. It doesn't protect other plants from gophers.
