So far we havn't seen a single mycelium patch anywhere on the server with the exception of around the starting deed.
There is plenty of towers with altars straight under them and multiple days have passed.
I asked players who played as hots on the latest elevation about it and acording to them the mycelium never spawned by itself, it only expanded from excisting mycelium and had to be "seeded" by priests.
From my knowledge mycelium is supposed to spread when domain and influence is present. Thus im reporting this.