The sweet potato does grow underground. This popular tropical and subtropical vegetable develops its edible portion entirely beneath the soil surface, similar to carrots and beets. The sweet potato, scientifically known as Ipomoea batatas, is one of the world’s most widely consumed crops, valued for its high carbohydrate content and nutritional value. Its underground growth is a biological strategy for the plant to store energy for survival and future growth. Sweet potatoes are harvested by digging them out of the ground after the above-ground vines have matured.
The Botanical Classification of Sweet Potatoes
The sweet potato is botanically classified as a storage root, which distinguishes it from other vegetables that grow underground. It belongs to the morning glory family, Convolvulaceae. This storage root is an enlarged, modified lateral root that the plant uses to accumulate starches and sugars produced through photosynthesis. The plant’s structure includes fibrous roots for absorption and specialized lateral roots that swell to become the edible part.
This classification means the sweet potato is a true root structure, not a modified underground stem. The purpose of this enlarged root is to provide a dense reservoir of nutrients. Unlike above-ground stems, a root structure lacks nodes or internodes, which are features associated with branching or budding.
The Underground Development Process
Sweet potatoes are typically propagated not by planting seeds, but by using “slips,” which are sprouts taken from a mature storage root. These slips are young cuttings planted directly into the soil after the danger of frost has passed. Once planted, the slips establish a root system, and certain lateral roots begin to thicken and expand, forming the storage roots that will eventually be harvested.
The successful enlargement of these roots requires specific conditions within the soil environment. Loose, well-drained soil is necessary, as dense or waterlogged soil can restrict the expansion of the developing storage roots and cause them to become misshapen. The underground portion of the plant focuses its energy on filling these roots with starch and sugar, allowing them to grow into their elongated, fleshy form. The entire growth period, from planting the slip to harvesting the mature root, often takes between 90 and 120 days.
Distinguishing Sweet Potatoes from True Potatoes
The sweet potato is frequently confused with the common white potato, but they are different botanically, despite both growing underground. The common potato, Solanum tuberosum, is a stem tuber, meaning it is a modified underground stem. Stem tubers possess “eyes,” which are nodes or bud sites that can sprout new stems and leaves.
While both are storage organs, their origin differs: one is an enlarged root, and the other is a swollen stem. Furthermore, the two vegetables belong to entirely different plant families. The sweet potato is in the morning glory family, while the true potato is a member of the nightshade family.