Poisonous potatoes. Selection of large, raw potatoes with some showing green colouration. The green colour indicates that the potatoes contain the poisonous alkaloid solanin, which occurs throughout the potato plant (Solanum tuberosum). Normal coloured potatoes contain only a trace of the poison, which is destroyed by cooking. If left in sunlight however, potatoes start to turn green and the level of the poison rises. A native of South America, the potato was introduced to Europe in the mid-16th century, and is now one of the world's most important foods. The edible part of the plant is the tuber, an underground swelling of the stem. The inseyesins are dormant buds.