Bishopweed. One hard plant to get rid of. You have to dig it out with all the roots, repeating this process may be needed since its hard to get all of the roots out. Or constantly mowing them down will eventually work too, but this may take a few years and mostly work if its a lawn area or such they inhabited. Planting a more desired ground cover is also a good way to go.
My neighbour tried to kill a patch with several strong treatments of RoundUp... They are bigger and meaner than ever before after thoose treatments, its one hard plant to kill.
Also important you don't let them flower or they may spread even faster, and to new parts of the garden. I still havnt got rid of them completely.
Its supposed to be edible, but my tastebuds does not agree.
Nature does not hurry, yet everything is accomplished - Lao Tzu