Cassava

Manihot esculenta (commonly called cassava) is a woody shrub, native to south America, of the spurge family, Euphorbiaceae. It is extensively cultivated as annual crop in tropical and subtropical regions for it's edible starchy tuberous root, a major source of carbohydrates. Though it is often called in Spanish and in the United States, it differs from the yucca, an unrelated fruit-bearing shrub in the family Asparagaceae. Cassava, when dried to a powdery (or pearly) extract is called tapioca, fermented, flaky version is named garri.
                                                 Kingdom - plantae
                                                   Clade - Angiosperms
                                                      Clade - Eudicots
                                                        Clade - Rosids
                                                           Order - Malphighiales
                                                             Family - Euphorbiaceae
                                                               Genus - Manihot
                                                                  Specie - M.esculenta
Cassava is the third- largest source of food carbohydrate in the tropics, after rice and maize. Cassava is a major stable food in the developing world, providing a basic diet for over half a billion people. It is one of the most drought tolerant crops, capable of growing on marginal soils. Nigeria is the worlds largest producer of cassava, while Thailand is the largest exporter of dried cassava.Cassava is classified as either sweet or bitter.Like other roots and tubers,both bitter and sweet varieties of cassava contain anti nutritional factors and toxins, with the bitter varieties containing much larger amounts.It must be properly prepared before consumption as improper preparation of cassava can leave enough residual cyanide to cause acute  cyanide intoxication, goiters, and even ataxia, partial paralysis, or death. The more toxic varieties of cassava are a fall-back source (a "food security crop") in times of famine or food insecurity in some places. Farmers often prefer the bitter varieties because they deter pests, animals, and thieves.
                                     Description
The cassava root is long and tapered with firm, homogeneous flesh encased in a detachable rind, about 1mm thick, rough and brown on the outside. Commercial cultivars can be 5 to 10cm (20 to 3.9 in) in diameter at the top, and around 15 to 30 (5.9 to 11.8 in) long. A woody vascular bundle runs along the roots axis. The flesh can be chalk-white or yellowish. Cassava roots are very rich in starch and contain small amounts of calcium (16mg/100g) phosphorus, (27mg/100g) and vitamin C (20.6mg/100g). However, they are poor in protein and other nutrients. In contrast, cassava leaves are a good source of protein (rich in lysine) but deficient in  the amino acid methionine and possibly tryptophan.