Dioscorea is a genus which includes many species. They grow as lianas that can become 2 to 12 meter tall.
Several species within the Dioscorea genus produce edible tubers which are called yams. Important yam species include Dioscorea rotundata, D. cayenensis, D. alata, D. opposita, D. bulbifera, D. esculenta, D. trifida and D. dumetorum.
Yams are common in West Africa and New Guinea.
Sometimes the sweet potato (Ipomoea batatas) is called yam, which can create some confusion.