Cassava

A perennial shrub usually grown as an annual, 1–3 m tall. The leaves are alternate and deeply palmately lobed, usually with three to nine lobes (mostly five), on long petioles; the stems show conspicuous leaf scars. Flowers are unisexual, small, petalless, in panicles. The tuberous roots swell at the underground nodes and store much starch; they are the main harvested part. The roots and leaves contain cyanogenic glycosides (mainly linamarin) that can release hydrogen cyanide when damaged, so they must be soaked, fermented, dried or thoroughly cooked before eating. There are two main cultivar groups: 'sweet' (low cyanide) and 'bitter' (high cyanide, suited to industrial processing).

Cassava originates in tropical South America (Brazil, Paraguay and the Andes) and has been cultivated for about 5,000 years; archaeological remains date to about 2,700 BCE in Venezuela and about 2,000 BCE on the Peruvian coast. In the 16th century the Portuguese took it to Africa and Asia. Today Nigeria is the largest producer, followed by Thailand; because it tolerates drought and poor soil, it is a key food-security crop. In Vietnam, cassava is grown mainly in Tây Ninh, Đồng Nai and Gia Lai; it is eaten boiled or steamed, made into cassava cakes and sweet soup, and processed into tapioca starch used for cakes and the food industry; the roots are also a feedstock for ethanol.