The potato is a starchy, tuberous crop from the perennial nightshade Solanum tuberosum L. The word "potato" may refer either to the plant itself or to the edible tuber.[2] In the Andes, where the species is indigenous, there are some other closely related cultivated potato species. Potatoes were introduced outside the Andes region approximately four centuries ago,[3] and have since become an integral part of much of the world's food supply. It is the world's fourth-largest food crop, following maize, wheat, and rice.[4] The green leaves and green skins of tubers exposed to the light are toxic.