Semi poison plants are more common than you might think. Leaves of potatoes can cause serious gastric disturbance. Rhubarb leaf blades can cause coma, seizures and difficulty in breathing. Workers harvesting cashews need to wear gloves lest the harmful oils in the rest of the plant cause a serious rash on their skin. Fruits of the majestic saguaro cactus of the Southwestern US and northwestern Mexico are prized for their luscious flesh that tastes rather like strawberries, yet the tissue inside the stems of the same plant contain powerful hallucinogens. The silks of maize contain cardioactive glycosides.Many stone fruits in the genus Prunus are also partly poisonous. This includes 400 species around the world, most of them referred to as cherries, but others as peaches, plums, nectarines or apricots. These are prize edibles that contribute a significant percentage of the food consumed by humans every day. Yet these valuable trees contain poisons lurking in the leaves and seeds. If you scratch the bark from a small cherry twig, especially in the spring, you can smell the scent of burnt almonds. This is amygdalin, a glycoside that reacts with enzymes inside the digestive tract to release cyanide.The stone fruit “stone” is actually the seed contained inside a hard, protective layer. Break it open to find the seed. But do not eat these seeds, as they contain amygdalin as well.Image: Robyn Mackenzie/Shutterstock