Our next Plant of the Month focuses on a larger grouping of plants with similar growth forms: potatoes (Solanum tuberosum), sweet potatoes (Ipomoea batatas), and yams (Dioscorea spp.).

Prior to our industrialized food system, stored foods like roots and tubers were important components of diets in winter and early spring, before other fresh fruits and vegetables were available. These roots and tubers could be stored in cool, dry places, but other species native to North America – such as tuckahoe (Oriontium aquaticum), cattail (Tyhpa sp.), arum (Peltandra virginica), groundnut (Apios americana), greenbrier (Smilax sp.), and Jerusalem artichoke (Helianthus tuberosus) – could have been harvested any time the ground was not frozen, although they are generally more nutritious between late fall and early spring.

Roots and tubers are major players in cuisines throughout the world, and potatoes, sweet potatoes, and yams are perhaps the most famous and the most often confused.  These plants are similar in that they thrive through their underground rhizomatous or tuber-like root systems. Generally, tubers function as storage organs for the plants, providing energy and substance for regrowth through the form of starches.  These starches are also often good sources of energy for humans too, especially when cooked!  There are important differences among these three tubers as well.

Potatoes:

The ‘classic’ potato (Solanum tuberosum) belongs to the Nightshade Family, which includes other important crops like peppers, tomatoes, eggplant, and tobacco. The common potato and other plants of the Nightshade Family are generally identifiable based on the following plant characteristics:

1. Alternate leaf arrangement, often lobed and hairy or prickly
2. Flowers contain 5 sepals and 5 petals
3. Plant contains superior or raised ovaries (location of fruit development) producing seeds in the form of berries, drupes, or capsules

The potato was domesticated around 7000 years ago in the Andean region of South America. With the advent of global exploration and colonization, the potato was introduced to other parts of the world and quickly became a staple resource for many groups. The potato is often associated with the Irish due to the historical Irish Potato Famine (1845-1849). This famine (and Great Britain’s response to it) cut Ireland’s population in half through starvation or forced migration to the United States or Australia as the potato crop became diseased, obliterating the food and/or cash source for the majority of the already penniless population.

Yams:

Americans commonly use the names “sweet potato” and “yams” interchangeably, especially when referring to a popular Thanksgiving side dish, but these two tubers belong to completely different plant families. Yams (Dioscorea spp.) are one of the many tropical plants assigned to the Dioscoreaceae Family, or Yam Family, and are similar to the vining growth form of plants in the Convolvulaceae Family, to which sweet potato belongs. Plants in the Yam Family are generally identifiable based on the following characteristics:

1. Woody or tuber-like roots
2. Heart-shaped leaves, sometimes lobed
3. Flowers in clusters, generally at leaf axils of the plant

A true yam consists of a starchy edible root with higher moisture contents and more natural sugar than the common sweet potato.

Yams are native to Africa and Asia, particularly tropical areas, and have long been cultivated by peoples in these regions.  Enslaved Africans brought yams with them to the New World, establishing them as staples in tropical settlements. (Carney and Rosomoff 2009: 97)  The confusion between yams and sweet potatoes may be based in this relationship, as enslaved Africans may have referred to the New World sweet potatoes as ‘yams’ because of their similarity to the true yams they knew from Africa.

Sweet Potatoes:

Sweet Potatoes (Ipomoea batatas) and other plants of the Convolvulaceae Family, or Morning Glory Family, have ‘root tubers’, in contrast to the ‘stem tubers’ of yams and potatoes.4 Sweet potato plants are identifiable based on the following family characteristics:

1. Usually vining or climbing for growth
2. Flowers usually have fused petals with folds with a funnel-like shape
3. Leaves are generally alternate with either lobed or heart-like shapes

Peoples in Central and South America cultivated sweet potatoes roughly 5000 years ago, and although these tubers reached Oceania by 1000 years ago, sweet potatoes did not arrive in eastern North America until colonial times. Gabby Purcell, a doctoral student at UNC-Chapel Hill, is currently analyzing sweet potatoes and other tubers from historic Cherokee sites in the Southern Appalachians, dating to roughly 1750-1830. She is researching the ways Native Americans incorporated these tubers into their diets, perhaps replacing some of the native tubers.

Here at the McClung, we are also working on plans for a Southern Foodways Garden to highlight some of the plants cultivated in the Americas and brought to North America by enslaved Africans.  We are collaborating with several groups, including Dr. Mike Ross and his students in the School of Landscape Architecture; the UT Chapter of Minorities in Agriculture, Natural Resources, and Related Sciences; UTK Native American Student Association; UTK African Student Association; and the Ecology and Evolutionary Biology Greenhouse.  We may try to grow sweet potatoes and yams here on campus, so please keep an eye for that!

In the meantime, here is a favorite recipe for sweet potatoes from Chris Weddig, our Exhibits Preparator and Coordinator here at the McClung.

Smoked Chile Scalloped Sweet Potatoes

Ingredients:

• 2 cups heavy cream
• 1 heaping tbsp chipotle pepper puree
• 3 medium sweet potatoes, peeled and thinly sliced 1/8-inch thick
• Salt and freshly ground black pepper

Directions:

Preheat oven to 375 degrees F.

Whisk together cream and chipotle puree until smooth.

In a 9-x-9-in casserole dish, arrange the sweet potatoes evenly. Drizzle with 3 tablespoons of the cream mixture and season with salt and pepper. Repeat with the remaining potatoes, cream, and salt and pepper to form 10 layers.

Cover and bake for 30 minutes; remove cover and continue baking for 45 minutes to 1 hour, or until the cream has been absorbed and the sweet potatoes are cooked through and the top is browned.  Enjoy!

References:

What’s Cooking America. 2021. “Potatoes – History of Potatoes.” Electronic document, https://whatscookingamerica.net/History/PotatoHistory.htm, accessed March 2021.

What’s Cooking America. 2021.”Sweet Potatoes.”  Electronic document, https://whatscookingamerica.net/sweetpottip.htm, accessed March 2021.

Petruzzello, Melissa. 2021. “What’s the Difference Between Sweet Potatoes and Yams?” Brittanica, electronic document, https://www.britannica.com/story/whats-the-difference-between-sweet-potatoes-and-yams, accessed March 2021.

Carnegie Museum of Natural History. 2020. “Potatoes, Sweet Potatoes, and Yams: What’s the Difference?” Electronic document, https://carnegiemnh.org/potatoes-sweet-potatoes-yams-whats-difference/, accessed March 2021.

For further reading:

Carney, Judith A. and Richard Rosomoff. 2009 In the Shadow of Slavery: Africa’s Botanical Legacy in the Atlantic World. University of California Press. Berkeley, California.

Edge, John T. (Ed.). 2007 The New Encyclopedia of Southern Culture: Volume 7: Foodways.  University of North Carolina Press. Chapel Hill, North Carolina.

Elpel, Thomas J. 2018 Botany in a Day: The Patterns Method of Plant Identification 6th ed. HOPS Press, LLC. Pony, Montana.

Fernald, Merritt and Alfred Kinsey. 1943 Edible Wild Plants of Eastern North America. Harper & Row Publishers Inc. New York City, New York.

Flora of North America Association. 2009. Flora of North America. Flora of North America Association (Producer). Available: http://www.fna.org/FNA.

Gucker, Corey L. 2009. Dioscorea spp. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.fed.us/database/feis/plants/vine/diospp/all.html.

Lachlin, Lucinda. 2021. Dioscorea species (Dioscoraceae). BRAHMS Online, Department of Plant Sciences, University of Oxford. Available: https://herbaria.plants.ox.ac.uk/bol/plants400/Profiles/CD/Dioscorea