I know this might sound like a stupid idea but what if there was a faction similar to the cult in Fallout 3 centered around a character who went full plant mutation that has rooted himself to the ground permanently?
The character rooted would start creating his own creep tiles similar to fungal blooms. This creep could boost plant growth/ create pitcher plants in deep pits to eat zombies before closing and acting like a “plank’d” pit for a day or 2, or just spawn Allied plants to defend his “flock”.
They’d be more or less druids using whatever clothing you want but probably leather with wood armour and for weapons they might use melee or archery to attack you.