most books I have awaiable say that all lichen are eadible… Thats not true!!!
Letharia vulpina, which grows in few parts of switzerland, sweden and in the north of the US has been used to poisen wolfs (there the name comes from). I have eaten it but didn’t feel any specific effect (I was in a bad shape when I ate it, so I dont know if it had some effect) Some author wrote that the vulpin acid only reacts in the metabolism of carnivores, so when I ate the vulpina I had not eaten meat for a week —> So, did i survive because of a flora diet???
All the references I’m familiar with say that letharia vulpina (wolf lichen) is poisonous. Which is what I have always heard. In this part of the world it has been used as a yellow dye.
One book says that in N. Europe it was mixed with wolf bait.
I don’t know the answer to your question. Maybe it was your lucky day. Maybe your dosage was too small. Maybe you were mistaken on your identification of it and it was really usnea. Were you trying to make yourself sick?