the secondary leaves are complete (torn in photo) ; all leaves are toothed; i think the stem may be square but it is so thin snd fleshy that it is hard to tell. ive never seen a flower but it comes to my attention in spring and ive not looked later in season.

Ground Elder, Aegopodium podagraria. Sorry to say it's a horrendous thug.

Yes the worst thug there is. I do hope it is not in your garden. If it is my condolences and dig deep...for years to come.

Of course

and i planted from moms garden decades ago; she warned me…,