Yam

Not a sweet potato

The “yams” sold in American supermarkets are almost always orange-fleshed sweet potatoes (Ipomoea batatas) — a different plant family entirely. True yams (Dioscorea) are a genus of climbing vines native to Africa and Asia, producing large starchy tubers with rough bark-like skin and dry, off-white flesh.

The naming confusion dates from the 1930s, when American sweet potato farmers wanted a marketing distinction for newer orange varieties and borrowed the African word nyami (yam). The U.S. Department of Agriculture later required dual labeling — “sweet potato” alongside “yam” — but the original misnomer is now nearly impossible to dislodge from American English.

Outside the U.S., this confusion mostly doesn’t exist. The British, African, Caribbean, and Asian use of “yam” almost always refers to the actual Dioscorea.

A cultural staple

Yams are central to many West African cuisines, especially in Nigeria, Ghana, and Benin. Pounded yam (iyan in Yoruba, fufu in many languages) is a staple meal:

1. Yam tubers are peeled and boiled until soft.
2. Pounded with a heavy mortar and pestle until smooth, sticky, and elastic.
3. Eaten with stews — egusi, efo riro, ogbono.

The pounding is hard physical work; modern households use mechanical pounders or pre-prepared yam flour. The texture — chewy, almost dough-like — is unique among starches and quite different from any potato preparation.

A real giant

Yams can grow large. The world record was over 130 kg, set in Nigeria. A typical commercial yam is 2–10 kg, larger than most sweet potatoes. A single tuber can feed a family for several days.

The New Yam Festival (Iri-ji) in Igbo culture, held annually in late August or early September, marks the end of the cultivation season and celebrates the first new yam harvest. It’s one of the most important traditional festivals in southeastern Nigeria.

The other “yam”

In Japan and Korea, yamaimo (Chinese yam, Dioscorea polystachya) is eaten raw, grated into a sticky white pudding called tororo, served over rice or soba. The texture is unlike anything else — slimy yet crisp, slightly sweet — and it’s an acquired taste even within Japan.

A diosgenin source

Several wild Dioscorea species (especially Mexican wild yam, D. villosa) contain diosgenin, a steroidal saponin that was historically the starting material for synthesizing progesterone and estrogen — the basis for early oral contraceptives. The work of Russell Marker in the 1940s, who perfected the synthesis from Mexican wild yam, is sometimes credited with making the birth control pill possible.