At least in Finland this is common knowledge and pretty much every house has rhubarb growing in the yard somewhere.

I'm living in Finland, and that is where I got that knowledge from. So yes, unfortunately my source is also empirical knowledge.

But knowing how certain African cultures learned to neutralize Cassava, and that knowledge passed through generations without knowing the reason why, I learned to not fully dismiss these kinds of knowledge...

Interesting. I'm in New Zealand and hadn't come across this. Being a commonwealth country makes me suspect it's not common knowledge in England either. Or has perhaps as you mention the reasons have been lost over time.

Thank you for your reply.