The sweet potato is a widely consumed crop, but its botanical classification is often confused with the common white potato. This confusion arises because “tuber” is generally used to describe any underground storage organ. Although both are starchy underground vegetables, they originate from different parts of the plant and belong to separate botanical families. Clarifying this distinction requires determining whether the sweet potato is a true stem tuber or a modified root structure.
Defining the True Tuber
A true tuber is a specialized, swollen, underground stem that stores nutrients, allowing the plant to survive dormant periods. Structures like the common white potato (Solanum tuberosum) are modifications of a stolon, a horizontal stem growing just below the soil surface. The fundamental characteristic identifying a true tuber as a stem is the presence of nodes and internodes.
These nodes are visible on the surface as the “eyes” of the potato, and each contains a bud capable of sprouting new stems and leaves. When exposed to light, these eyes produce new green shoots, confirming they are stem tissue. The internal structure also contains parenchyma cells that store large amounts of starch to fuel the plant’s regrowth.
The Sweet Potato’s True Identity
The sweet potato (Ipomoea batatas) is classified as a storage root, sometimes called a tuberous root, and is not a true tuber. The edible part is a modification of the root system, specifically a lateral root, rather than a modified stem. The plant belongs to the morning glory family, Convolvulaceae, placing it in a different botanical group from the white potato.
Storage roots are created when the plant’s fibrous roots thicken to accumulate starches and sugars. Unlike the stem tuber, the sweet potato storage root lacks the characteristic nodes or “eyes” needed to sprout new stems directly from its surface. Reproduction is accomplished via adventitious roots that form from stem cuttings, known as “slips,” which are then planted. The purpose of this enlarged structure is nutrient storage, which gives the sweet potato its fleshy, tapered shape.
Distinguishing Sweet Potatoes from Yams and Potatoes
Market confusion often groups three distinct botanical structures: the stem tuber, the storage root, and the true yam tuber. The white potato (Solanum tuberosum) is a stem tuber characterized by its eyes and belonging to the nightshade family. The sweet potato (Ipomoea batatas) is a storage root structure with a smooth, thinner skin.
A true yam, belonging to the genus Dioscorea, is also a stem tuber but is botanically distant from both the sweet potato and the white potato. True yams are typically drier, starchier, and possess a rough, bark-like skin, often growing to larger sizes. In the United States, orange-fleshed sweet potatoes were historically called “yams” to distinguish them from firmer varieties, but this is a misnomer. Due to this confusion, the U.S. Department of Agriculture requires any sweet potato labeled as a “yam” to also be identified as a sweet potato.