The peanut, Arachis hypogaea, is a globally important crop that provides protein and oil. Despite its common name, the peanut is a legume, placing it in the same plant family as peas and beans. Its growth habit is unique, exhibiting a reproductive process called geocarpy, meaning the fruit develops underground rather than above the soil surface. This subterranean development protects the seed and influences the structure of the surrounding shell. The appearance of the peanut seed, or kernel, reflects its function as a high-energy storage unit for the next generation of the plant.
Visual Description of the Peanut Kernel
The peanut kernel is the seed itself and is typically oblong or somewhat kidney-shaped, though its exact size and form depend significantly on the cultivar. Varieties like the Runner group tend to produce medium-sized, uniform kernels, while the Virginia group produces the largest seeds. The Spanish and Valencia types are often smaller and rounder in shape.
The most noticeable external feature is the seed coat, or testa, a thin, papery layer that tightly encases the kernel. This testa can display a range of colors, which distinguishes different peanut types. While pinkish-tan or light red is common, the testa can also be deep red, purple, black, or white, with some varieties exhibiting a variegated pattern.
Beneath the testa, the kernel is dominated by two large, fleshy halves, which are the cotyledons. These cotyledons store the food reserves—high levels of oil and protein—that the embryo will use during germination. Tucked between them is the tiny embryonic axis, which contains the radicle and plumule that will develop into the root and shoot of the new plant.
The Structure of the Protective Pod
The shell that surrounds the kernels is technically the fruit of the peanut plant, known as a pod or a legume. This protective casing develops underground after a specialized stalk, known as a peg, elongates and pushes the fertilized ovary downward into the soil. The subterranean environment influences the pod’s structure, which is rough, netted, and wrinkled on its exterior surface.
The pod’s texture is often described as having a characteristic reticulated pattern across its length. Inside the shell, the kernels are held in individual compartments, usually two or three per pod, although some types may contain up to five seeds. These compartments are separated by constrictions in the shell, which make the pod look segmented.
The pod wall is composed of a tough, fibrous material that provides a barrier against the soil and pests. The process of geocarpy requires the ovary to penetrate the soil, meaning the pod’s structure is designed to withstand physical pressures and moist conditions. Pods will not fully develop unless they successfully penetrate the soil.
Preparing the Seed for Planting
Peanut kernels sold roasted for consumption are not viable seeds. For successful propagation, raw, unshelled peanuts from a seed supplier or specialty market are necessary. The seed must be carefully removed from its shell immediately before planting, as shelling too early can reduce viability.
It is important to handle the kernel gently to ensure the papery seed coat, or testa, remains completely intact. This testa acts as a protective layer against damage and disease, and its removal or tearing can compromise the seed’s ability to germinate. The tiny embryonic axis, or germ, is particularly susceptible to physical injury during shelling and planting.
To promote germination, the shelled seeds should be planted in warm, loose soil, requiring a minimum average temperature of 65°F. Planting into warm, loose soil ensures rapid and uniform emergence for a strong start. The seed is typically placed about two inches deep, creating a favorable environment for the radicle to emerge and the cotyledons to unfold.