I'm trying to find the name of a science-fiction book I read at least 20 years ago (late 1990s), though it was most likely a second hand book so I can't say how much older than that it might be. I can only remember a few details though some are quite specific:
- It was mostly (possibly completely) set on a recently colonized planet (not in our solar system)
- The planet had some kind of plant or fungus that covered most of the surface
- This plant formed some kind of symbiotic link with the human colonists, making them more empathetic and reduced conflict
- There was some kind of galaxy spanning religion that was specifically against forms of mind control (and so distrusted what this plant was doing)
- One very specific part of this religion I can remember, is that the members didn't cut their hair because someone long dead that they viewed as a prophet said something along the lines of "Don't let anyone mess with your head" which they took to mean condemn mind control plus don't cut your hair!
The only other thing I can remember is that this plant/fungus was completely benign and I think ended up with one of the religious types being "infected" and realizing this.