Yam is the common name for some plant species in the genus Dioscorea (family Dioscoreaceae) that form edible tubers (some other species in the genus being toxic).
Yams are perennial herbaceous vines native to Africa, Asia, and the Americas and cultivated for the consumption of their starchy tubers in many temperate and tropical regions. The tubers themselves, also called "yams", come in a variety of forms owing to numerous cultivars and related species.
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A staple food, food staple, or simply staple, is a food that is eaten often and in such quantities that it constitutes a dominant portion of a standard diet for an individual or a population group, supplying a large fraction of energy needs and generally forming a significant proportion of the intake of other nutrients as well. For humans, a staple food of a specific society may be eaten as often as every day or every meal, and most people live on a diet based on just a small variety of food staples. Specific staples vary from place to place, but typically are inexpensive or readily available foods that supply one or more of the macronutrients and micronutrients needed for survival and health: carbohydrates, proteins, fats, minerals and vitamins. Typical examples include grains (cereals and legumes), seeds, nuts and root vegetables (tubers and roots). Among them, cereals (rice, wheat, oat, maize, etc.), legumes (lentils and beans) and tubers (e.g. potato, taro and yam) account for about 90% of the world's food calorie intake.
Early agricultural civilizations valued the crop foods that they established as staples because, in addition to providing necessary nutrition, they generally are suitable for storage over long periods of time without decay. Such nonperishable foods are the only possible staples during seasons of shortage, such as dry seasons or cold temperate winters, against which times harvests have been stored. During seasons of surplus, wider choices of foods may be available.
Taro (/ˈtɑːroʊ, ˈtær-/; Colocasia esculenta) is a root vegetable. It is the most widely cultivated species of several plants in the family Araceae that are used as vegetables for their corms, leaves, stems and petioles. Taro corms are a food staple in African, Oceanian, East Asian, Southeast Asian and South Asian cultures (similar to yams).
Tubers are a type of enlarged structure that plants use as storage organs for nutrients, derived from stems or roots. Tubers help plants perennate (survive winter or dry months), provide energy and nutrients, and are a means of asexual reproduction.
Stem tubers manifest as thickened rhizomes (underground stems) or stolons (horizontal connections between organisms); examples include the potato and yam. The term root tuber describes modified lateral roots, as in sweet potato, cassava, and dahlia.
The sweet potato or sweetpotato (Ipomoea batatas) is a dicotyledonous plant in the morning glory family, Convolvulaceae. Its sizeable, starchy, sweet-tasting tuberous roots are used as a root vegetable, which is a staple food in parts of the world. Cultivars of the sweet potato have been bred to bear tubers with flesh and skin of various colors. Moreover, the young shoots and leaves are occasionally eaten as greens. The sweet potato and the potato are only distantly related, both being in the order Solanales. Although darker sweet potatoes are often known as "yams" in parts of North America, they are even more distant from actual yams, which are monocots in the order Dioscoreales.
The sweet potato is native to the tropical regions of South America in what is present-day Ecuador. Of the approximately 50 genera and more than 1,000 species of Convolvulaceae, I. batatas is the only crop plant of major importance—some others are used locally (e.g., I. aquatica "kangkong" as a green vegetable), but many are poisonous. The genus Ipomoea that contains the sweet potato also includes several garden flowers called morning glories, but that term is not usually extended to I. batatas. Some cultivars of I. batatas are grown as ornamental plants under the name tuberous morning glory, and used in a horticultural context. Sweet potatoes can also be called yams in North America. When soft varieties were first grown commercially there, there was a need to differentiate between the two. Enslaved Africans had already been calling the 'soft' sweet potatoes 'yams' because they resembled the unrelated yams in Africa. Thus, 'soft' sweet potatoes were referred to as 'yams' to distinguish them from the 'firm' varieties.
Dioscoreaceae (/ˌdaɪəˌskɔːriˈeɪsii/) is a family of monocotyledonous flowering plants, with about 715 known species in nine genera. The best-known member of the family is the yam (some species of Dioscorea).
The APG system (1998) and APG II system (2003) both place it in the order Dioscoreales, in the clade monocots. However, the circumscription changed in the APG II system, with the 2003 system expanded to include the plants that in the 1998 system were treated in the families Taccaceae and Trichopodaceae.