Master Gardener: A yam is not always a yam

If your guests are tired of arguing about politics at the Thanksgiving table, try discussing the candied yams on their plates. Are they really yams? If you want to win the argument, read on. Be ready to explain that sweet potatoes and true yams are profoundly different. They even belong to different plant families. According to Wikipedia, "Yam is the common name for several plant species in the genus Dioscorea (family Dioscoreaceae) that form edible tubers …" The tubers (also called yams) of more than 600 varieties have different textures/colors/shapes/sizes. Real yams are African and Asian natives whose tubers can vary in size from a normal white potato to enormous tubers weighing 100 pounds and measuring as much as 60 feet in length. True yams are the third-most important tropical root crop after cassava and sweet potatoes. Of the worldwide crop, 95 percent is harvested in West Africa. True yams can be stored for very long periods of time, making them an important crop for when food is in short supply. One Dioscorea species called Air Yams (Dioscorea bulbifera) has tubers called bulbils on its stems as well as underground tubers. Eating them can be poisonous unless properly boiled. Air Yams are a West Africa food crop growing wildly in every county in Florida. It can quickly propagate and grow more than 60 feet, overtaking native flora in Florida. Introduction, possession, propagation and movement of this species are prohibited by law in Florida, Alabama and Hawaii unless you have a permit. It has naturalized also in warmer parts of Texas, Mississippi and Georgia. Yikes! But in areas where it can't survive the winters, it is considered a lovely ornamental annual. Another wildly invasive species is the cinnamon or Chinese yam (D. polystachya) which can be grown in USDA Zones 5-10. Bad news. This one will survive the winters in more states, including California's Sierra foothills. Currently, it ranges from Vermont to Georgia and west to Oklahoma and Texas. Hold the line! Probably the most cultivated, edible, true yam is the white yam or water yam (D. alata). Tubers can grow to 8 feet in Zones 9-11. (We are Zone 9.) They can also weigh up to 100 pounds if left unharvested. And yes, this invasive species is also a threat to native plants. Sweet potatoes are a vine species (Ipomoea batatas) in the morning glory family (Convolvulaceae). They are grown widely in the U.S. as annuals and in Zones 9-11 (Auburn) as perennials. They've been around for centuries, in Central and South America, for 5,000 years. When Columbus arrived in Haiti, he encountered sweet potatoes called batatas by the native people there. Sweet potatoes are a "two-for-one" crop: leaves as well as tubers are tasty. It also has a "two-for-one" function: food crop and landscape beauty. In our miserable summer heat here in the Auburn area, we can quickly grow a sweet potato lush groundcover with morning glory-type flowers and find it at local nurseries. If you want to grow sweet potatoes, make sure the planting soil is roomy enough (8-12 inches) to grow a good-size root tuber. Place compost upon planting area in the fall. Plant in spring in the full sun; this tropical plant loves the heat. It also requires medium moisture, well-drained acidic soil. For more info: https://mgsantaclara.ucanr.edu/garden-help/vegetables/sweet-potatoes/. Sweet potatoes, like real yams, come in various shapes, sizes and colors. For market use, they are classified as "dry-fleshed" or "moist-fleshed," according to the feel sensation experienced in the mouth when eating a cooked or baked sweet potato. AND HERE COMES THE SHOCKING NEWS: The "moist-fleshed" sweet potato is sometimes referred to as a "yam" and the "dry-fleshed" as a "sweet potato." They are, however, both sweet potatoes. It's very likely everyone at the table has never eaten a real yam. Gently tell your guests everything produced and sold in the United States as a yam is really a sweet potato. (Some true yams are imported here from Africa, but they are not sold by the average grocery retailers.) The USDA now requires any label with "yam" to also include "sweet potato." For some people, the labeling confusion is a sore spot since it doesn't conform to old family traditions and you may be met with passionate resistance. There's not much we can do to change the minds of the generations who have always revered sweet potatoes as yams. But you can take pleasure in educating the younger guests.