The largest herb in the world is the banana "tree". Since it never forms true wood, or even anything closely analogous to wood, it's not a tree but a herbaceous plant... admittedly, one that can grow to almost 8 meters tall!

What we call "a flower" isn't always just a flower. Often, it's actually a mass of several, tens, or even hundreds of tiny flowers -- an inflorescence -- condensed until it looks like one unit, sometimes with extra "petals" formed from tissues that aren't flowers at all. Jack-in-the-pulpit, dandelions and daisies, and poinsettias are all good examples of this particular weirdness.