I have this weed in my chile patch. It's shown up every year for quite a while 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 there's a very deep runner or something and it sends up plants from there. Round-up (desperate here) seems to kill the particular plant but not the entire system and its mothership. It roughly radiates outward from a point slightly 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 toughie.

https://imgur.com/a/X7O9a3Z