I have this weed in my chile patch. It's shown up every year for quite a wh ile and every year it's a little more invasive than the year before. I can cut it off pretty deep, several inches, and not hit its roots. I suspect th ere's a very deep runner or something and it sends up plants from there. Ro und-up (desperate here) seems to kill the particular plant but not the enti re system and its mothership. It roughly radiates outward from a point slig htly outside my property, on the other side of our fence.
I've never seen this before its first appearance in my garden. It's a tough ie.