B12 in chia seeds
I'm just wondering what the deal is with chia seeds. They are advertised as containing B12, but everywhere I've read has always said B12 doesn't naturally occur in plant foods. I know it is contained in spirulina and sometimes seaweed, which I assumed was due to the water environment containing it, but if these chia seeds do contain B12, why has it so often been said (in many sources) that you can't get it from plants?
To add to this, here in Australia, the brown mushroom bags provided in supermarkets say that mushrooms are a good source of B12. I find this bizarre and potentially quite misleading. I would think the only source of potential B12 in mushrooms would be the dirt on them.
Apologies if this has already been discussed - I couldn't find it in memories.