I'm not sure if you'd call this 'unsolved' or frankly even solvable. But there are two trees found in parts of Central America, called the Chechem tree and the Chaka tree. The Chechem tree's bark has a p****n that is so strong that just by touching the bark (or its sap of course) your skin will begin to numb. The cure to this exact p****n lies in its sister tree, the Chaka. And as if that wasnt enough all on its own, whats more they are Always found to be right next to each other in nature. There is a Mayan myth that comes with these trees that they are from two brothers that fought each other over the love of a woman, but they ended up unaliving each other, and the woman, Nicte-Ha, died of heartbreak. One of the brothers, Kinich, was kind and caring, and thus became the Chaka tree. The other brother, Tizic, was cold-hearted and arrogant, and became the Chechem tree. Poisons and cures found in nature are of course a reality in many different instances, but the fact that these trees are right next to each other in nature, and provide exactly opposite effects, is pretty crazy.