My favorite group were the Shepherds of the Root. They were a CN nature cult. They followed a goddess that thought civilization was a creation of the gods to keep mortals docile and under control. They're an odd mix of primitives and botanists. I think comparing them to the Batman villain Poison Ivy would be appropriate. One of the most fascinating thing about the cult members is that they all have a seed planted in their chest during a cult ritual (that involves the member being buried planted). When the member dies a plant creature springs forth from the corpse.
I want to include something like this in my 5th edition game. My version won't follow a specific deity, though they'll have allies among some of the wilder gods. I think I prefer the name "The Crushing Root." Barbarians, druids, and savages make up the wilderness faction and botanists, elves, and other potential eco-terrorists make up the "civilized" faction. The group and its overall goals do make chaotic neutral a suitable alignment choice, though I see some of the members being more chaotic evil. Definitely keeping the burying and seed in the chest ritual, along with the plant creature bursting forth upon death. Unlike the generic creature in the original book, I think the plant monsters that burst forth from my cultists will be varied. A good tactic in fighting the cultists is to use fire, since it would potentially harm the plant creature sprouting forth.
I think this group will be fun to use. Anyone else have any suggestions for my anti-civilization plant cult?