The potato plant, Solanum tuberosum, is an herbaceous perennial cultivated as an annual crop for its edible underground tubers. It belongs to the Solanaceae family, which also includes tomatoes, peppers, and eggplant. The above-ground portion is often referred to as a “vine,” though it does not climb like a true vine, instead forming a leafy, sprawling bush. Many of its parts, unlike the potato itself, contain toxic compounds like solanine.
Growth Habit and Stem Structure
The above-ground structure of the potato plant is a semi-erect, bushy form that typically reaches heights of one to three feet. It begins upright but tends to spread and flop over as it matures and the weight of the foliage increases.
The main stems that emerge from the soil are usually green and herbaceous, though they can sometimes exhibit purple or reddish pigmentation depending on the specific cultivar. A distinct feature of the potato stem is its angular or slightly square cross-section, rather than being perfectly round like many other plants. The stem surface can range from being relatively smooth to sparsely covered with fine hairs.
Below the soil line, the main stem produces specialized underground stems called stolons, which are thin and horizontal. The ends of these stolons swell significantly to form the tubers that are harvested for food. This characteristic confirms that the potato is a modified stem, not a root.
Foliage and Leaf Arrangement
The leaves of the potato plant are compound. This structure is described as pinnate, with leaflets organized in pairs along the central axis, culminating in a single terminal leaflet at the tip. The overall length of a mature compound leaf can be up to twelve inches.
A typical compound leaf usually displays between seven and eleven oval to oblong leaflets, though this number varies widely by variety. These leaflets often have smooth or slightly wavy margins. Smaller leaflets, known as interjected leaflets, may also appear between the larger pairs, giving the leaf a dense appearance.
The foliage is usually a medium to dark green color with a matte or slightly waxy texture. The leaves are arranged alternately along the main stems. When crushed, the leaves often emit a distinctive earthy or somewhat bitter scent, characteristic of the nightshade family.
Flowers and Toxic Fruit
Potato plants produce star-shaped flowers in clusters called cymes that form at the ends of the stems. Individual flowers feature five fused petals, typically about an inch across, with prominent, fused yellow stamens at the center.
Petal color can vary significantly across cultivars, including white, pink, purple, or light blue. Flowering signals that the plant has begun the process of tuber formation underground, although some modern varieties produce tubers without ever flowering. These flowers are primarily pollinated by insects, such as bumblebees.
If successfully pollinated, the flowers may develop into the plant’s fruit, which is a small, round berry resembling a miniature green tomato. These berries are usually less than an inch in diameter and contain numerous small seeds. These berries, along with the stems and leaves, are highly toxic due to their high concentration of solanine.
Key Distinctions for Safe Identification
Identifying the true potato plant, Solanum tuberosum, requires careful observation to distinguish it from related, and often highly poisonous, nightshades like deadly nightshade (Atropa belladonna). The potato’s stem is characteristically angular or square in shape, differentiating it from the rounder stems of many climbing vines.
The foliage structure is another telling feature, specifically the compound leaf with its terminal and paired lateral leaflets. This pinnate arrangement, coupled with the herbaceous, sprawling growth habit, contrasts sharply with the glossy, woody stems of ornamental species like jasmine nightshade (Solanum laxum), which is sometimes incorrectly called “potato vine”.
The fruit provides a final distinction; the potato’s small, green, tomato-like berry is a unique marker within the garden setting. Recognizing the precise morphology—the angular stem, the specific compound leaf structure, and the presence of the green berry—is the safest way to ensure correct identification.