While yams appear very similar to sweet potatoes, they’re quite different. In fact, they’re not even related. Yams belong to the Dioscoreae or morning glory family, while sweet potatoes are from the genus Convolvulaceae. Yams (from the African word “nyami,” meaning “to eat”) have only one embryonic seed leaf, while sweet potatoes have two.
Yams are grown throughout Africa, but Nigeria is the world’s most prolific producer, exporting to 70% of the world market. Close to 200 species of yams are eaten worldwide, but other than those found wrapped individually in supermarkets, they aren’t easily found on American produce shelves. Popular varieties include Hawaiian yam, Korean yam, and sweet yam.
Compared to sweet potatoes, yams are usually longer – sometimes as long as several feet – and not as sweet, having a rough, dark orange or brown surface that looks like tree bark. They’re usually harvested after a year of vine growth, dried for several hours in a barn ventilated for that purpose, after which they can be stored without refrigeration for several weeks.
Yams are thought to have originated in Asia, carried to Africa around the first century before being transported to the Caribbean with the slave trade.
Although they’re considered to be a starchy vegetable, yams are made up of complex carbohydrates and dietary fiber allowing for slow uptake to keep blood sugar levels even, giving it the nod as a low glycemic index food. The vitamin A that is converted into beta-carotene when eating yams isn’t as spectacular as those in sweet potatoes, but the antioxidants they provide are exceptional. The vitamin A in yams has other functions, such as maintaining healthy mucous membranes and skin, heightening night vision, supporting healthy bone development, and providing protection from lung and mouth cancers.