Root vegetables are plant roots used as vegetables. Other underground plants are often, erroneously, called root vegetables. Root vegetables include both true roots such as tuberous roots and taproots, but exclude non-roots such as tubers, rhizomes, corms, and bulbs. Several types contain both taproot and hypocotyl tissue, and it may be difficult to distinguish the two. Regardless of anatomical type, root vegetables are generally storage organs, enlarged to store energy in the form of carbohydrates. They differ in the concentration and the balance between sugars, starches, and other types of carbohydrate. Of particular economic importance are those with a high carbohydrate concentration in the form of starch. These starchy root vegetables are important staple foods, particularly in tropical regions. They overshadow the cereals throughout much of West Africa, Central Africa, and Oceania, where they are used directly or mashed to make foufou or poi.