You need to learn how to fight them because you will encounter their relatives (Jungle Lilies) in another dungeon. And it will be imperative to kill them.Basically, if you can engage ONE at a time you can actually use close ranged tactics. THe problem is that you usually can't split them up with any certainty. So they all breathe on you and that's pretty much that. It also seems to me that engaging them via ranged spells does not kick them into turn-based mode very easily. So yes, they are a real biatch.
The only way I found to kill them was to load up all my high damage AE spells, get fully buffed, then save the game. Then engage them from as far away as possible with as many volleys as possible. You should be able to get off many because they move slowly. Then, pray that the 3 (or whatever number) get stuck on each other in some sort of terrain feature like a narrow doorway or tree stand. If they do, just blast away with ranged spells. If they don't then RUN AWAY! Keep running and blasting. Sometimes you'll get lucky and they'll split up. If you can take the initial hit then you can melee them quite easily because they will have entered turn based mode. If none of that works, you'll die. Then you can reload and try again.
One other thing to try is dodging (with strafe keys) the breathe at the very last second. In some cases it works.