The spawn places are fixed. The alchemy plant that spawns in the node will vary.
Thanks to both of you, that makes sense. So if I see a mushroom node on the map, it could be any of them.
I'm trying to find more violet coprinus, but it's elusive. I have enough for now, but unfortunately, some of the alchemy writs require 3 of them, so eventually I'd run out if I didn't try to find more.