A plant of the genus Solanum in the nightshade family, Solanaceae; it is related to tomatoes and peppers. There are more than 2000 species of Solanum, of which about 150 bear tubers. The potato of commerce, S. tuberosum, originated in South America, probably in the highlands of Peru and Bolivia, where it has been cultivated for several thousand years. Potatoes were introduced into Europe by Spanish explorers in the late sixteenth century and into the United States from Ireland in 1719. The crop became a staple in Europe, was a primary source of food in Ireland, and is known even today as the Irish potato. The potato blight famine of 1845 and 1846, caused by Phytophthora infestans, was responsible for the death of more than a million Irish people, and the emigration of about 1.5 million others.