I'm more familiar with mushrooms than plants. But are a ton of plants that aren't served for various reasons. In terms of plants that aren't served specifically because they have a high likelihood of causing bad reactions, I'm not sure -- milkweed and certain species of fiddleheads might be good examples. There are lots of different reasons for why certain foods aren't commercially available, and often it's just completely arbitrary. E.g. the reason you can't buy coca tea is that Obama doesn't recognize religions different from Christianity as being valid. (His administration specifically lobbied the UN not to let South Americans use it for religious purposes.)
Interesting, I didn't know about the coca tea. I thought of another health-based one: unpasteurized milk and cheese. Generally not a problem in Europe, but highly regulated in some states (e.g. no raw milk cheese younger than 60 days, no raw milk period).
There are other animal-based ones that aren't really health related. E.g. restaurants aren't allowed to serve meat that's not FDA inspected, but the FDA only inspects a small variety of meats. There was a restaurant in SF that was serving cricket tacos and they got shut down because of this:
So yeah, the FDA caters to big industry, and the meat coming out of feedlots is scarier than your typical roadkill, but this is pretty well-known.
My understanding is that although there are a ton of regulations restricting the sale of food, the health reasons cited are generally dubious, rather than genuine.
The chicken-of-the-woods thing is obviously genuine, and I'd believe the same for a lot of different mushrooms. I've purchased about 20 species of wild fungi and I'm basically content with that variety. Raw milk / cheese I would say was a dubious health reason.
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