Flowers slightly smaller than a Dime US coin?
Weed grows primarily in the late summer to fall.....like now, but not noticeable other times of the year?
Single main root that is similar to a carrot in that it's thick and deep penetrating?
Off shoots from the main root are like a tree's canopy and very stemmy/wiry/hard?
If you answer yes to these questions, I have been trying to ID the weed too.