Cassava (Manihot esculenta). Watercolour artwork of a cassava plant. This perennial shrub is cultivated for its edible tubers which are a rich source of carbohydrate. Apart from this they have very little nutritional value, although the leaves of the plant are a rich source of protein. Like the potato, the cassava originates in South America where it is still a popular crop. It is also grown throughout Africa and Asia. Cassava is best eaten immediately after harvesting after which it is stored in water until cooking, to prevent the flavour from spoiling.