Cassava: Staple Root Crop of the World Tropics
Manioc (Manihot esculenta) is a ubiquitous Neotropical tree
grown for its tuber, a carbohydrate- rich root usually referred to
as cassava or yuca, which has become a staple food of humans
throughout the region (plates 11- 32– 33). A native of South
America, Manioc has long been grown throughout the tropical
world. A perennial, it will grow annually without replanting. It
is typically planted from cuttings taken from mature plants. For
consumption, the tuber is usually ground into a paste and made
into a hard bread, though it can also be fermented into a kind
of beer. Whole recipe books have been written about the use
of cassava. The plant itself is a small, spindly tree, with palmate,
compound leaves, most unpretentious in appearance. The root,
however, is thick and often more than 1 m (39 in) in length.On nutrient- poor soils, Manioc contains prussic acid, a powerful
cyanogenic glycoside that defends the root from herbivore
attack. Indigenous people have developed various methods
for removal of the prussic acid, an absolute necessity before
further preparation. In some cultures toxic cassava- root paste
is soaked in water and repeatedly squeezed and compressed—
literally wrung out; this washes the water- soluble cyanogenic
compounds from the paste, rendering the root safe to consume.
Many varieties of Manioc exist with variable levels of prussic
acid concentration. There are sweet varieties of cassava, with
essentially no prussic acid, and bitter cassava, which has high
concentrations of cyanide compounds. Sweet- tasting varieties
grow only in the most fertile soils, while the bitter strains are
found in soils of low fertility, where herbivore damage would be
more costly to the plant.The Cyanogenic Millipede: What’s That Almond Smell?
Plants are not the only organisms to utilize cyanogenic
compounds. Millipedes, members of the huge phylum
Arthropoda, are harmless ambling herbivores of the forest floor
(plate 11- 34); they should not be confused with swift- moving
carnivorous centipedes, which inject toxin when they bite
(chapter 16). Neotropical millipedes in the genus Nyssodesmus
appear armored with a flattened shiny carapace protecting
their delicate undersides. One of these creatures may reach 10
cm (4 in) in length and is readily visible as it slowly makes its
way about on the forest floor. These millipedes are common
throughout the Neotropics, and there is a probable reason as to
why— they are well protected.When threatened, these millipedes roll up in a ball and tough it
out (plate 11- 35). Some have an impressive array of chemicals
at their command. The hindgut can squirt a volley of noxious
liquid, containing both hydrogen cyanide and benzaldehyde.
You’ll notice this behavior if you handle one of these creatures,
and your hands will smell distinctly like almonds, from the
cyanide. Be sure to wash your hands afterward.Plate 11- 32. Manioc cutting, recently planted, will
grow into a full- size plant; its root is sold under the
name cassava. Photo by John Kricher.Plate 11- 33. Cassava (manioc root) for sale at a market
in Manaus, Brazil. Photo by John Kricher.Plate 11- 34. Millipede on forest floor. Photo by John
Kricher.Plate 11- 35. Millipede in the hand, curling into a ball.
Photo by John Kricher.190 chapter 11 evolutionary arms races: more coevolution, more complexity