• A tropical, virtually pure starch tuber up to 30 cm long of a plant, Manihot utilissima, which is grown in hot countries and used as a major carbohydrate source in South America, Africa and other countries. The roots of some varieties have to be grated and boiled in several changes of water, or partially fermented, to remove toxic cyanide compounds which are in the plant cells and are broken down by enzymes in the sap. The leaves are also edible and do not contain toxic compounds and are cooked as a vegetable or used as a food wrapping. Many people are permanently crippled by the poison especially in Africa.