Another image from the back streets of the Old City in Shanghai showing the yam (or sweet potato) seller in action.

Yam is the common name for some species in the genus Dioscorea (family Dioscoreaceae). These are perennial herbaceous vines cultivated for the consumption of their starchy tubers in Africa, Asia, Latin America and Oceania. There are many cultivars of yam.

The sweet potato (Ipomoea batatas) has traditionally been referred to as a yam in parts of the United States and Canada, but it is not part of the Dioscoreaceae family.

Although it is unclear which came first, the word yam is related to Portuguese inhame or Spanish ñame, which both ultimately derive from the Wolof word nyam, meaning “to sample” or “taste”; in other African languages it can also mean “to eat”, e.g. yamyam and doya in Hausa or “to chew” in Dholuo language of the Luo of Kenya and Northern Tanzania.

There are over 100 ethnic groups and languages in Nigeria, and each has different language names for Yam, “Isu” is the Yoruba translation or “Iyan” when it has been prepared to be consumed as a main course for dinner. The yam is a versatile vegetable which has various derivative products after process, it can be barbecued; roasted; fried; grilled; boiled; smoked and when grated it is processed into a dessert recipe. Yams are the staple crop of the Igbo people of Nigeria, in their language it is known as ji, and they commemorate it by having yam festivals known as Iri-ji or Iwa-Ji depending on the dialect.

Yam tubers can grow up to 2.5 m (8.2 ft) in length and weigh up to 70 kg (154 lb).

The vegetable has a rough skin which is difficult to peel, but which softens after heating. The skins vary in color from dark brown to light pink. The majority of the vegetable is composed of a much softer substance known as the “meat”. This substance ranges in color from white or yellow to purple or pink in ripe yams.

Yams are a primary agricultural commodity in West Africa and New Guinea. They were first cultivated in Africa and Asia about 8000 B.C. Due to their abundance and consequently, their importance to survival, the yam was highly regarded in Nigerian ceremonial culture and used as a vegetable offered during blessings.

Yams are still important for survival in these regions. The tubers can be stored up to six months without refrigeration, which makes them a valuable resource for the yearly period of food scarcity at the beginning of the wet season.

Yams are used as food plants by the larvae of some Lepidoptera species including Palpifer sordida.