tenngun mentioned Blow fish. I ate hundreds of blow fish before I found out there was a toxin in them. Elderberry plants have a toxin, the lower on the plant, the higher the toxin. Roots will kill some livestock. Polar Bear liver is suppose to have so very much Vitamin D, that a few drops of juice from the liver on the meat can be lethal. May apples are said by some to be so tastely when ripe, but also full of a chemical that causes most people severe gastric distress. Wild cherries are supposed to be toxic, but old timers around here claimed they were good for an upset stomach.
We ate dandelions for salad in early March when they first start growing. Later in the season they are too tough and bitter. There is a big debate over whether the annual known as huckle berries (not blue berries) are toxic. I have read that they are toxic to most, that they are not toxic if cooked first, and that the berries are not toxic but the plant is. Milkweed was eaten by old timers around here, but the milky white sap is supposed to be toxic until cooked and rinsed away.
When I was a kid, my great grandfather loved Jerusalem Artichokes. He would eat second and third helpings with no problem. Every time I have tried them, I got horrible intestinal cramps. In his journal, Lewis made reference to a root that Sacagewea showed them to eat, that many in the party developed such intestinal problems from.
