The coconut, often seen in tropical regions and grocery stores, is commonly referred to as a nut, but is technically a fibrous one-seeded drupe, a type of fruit similar to a peach or an olive. This unique botanical identity helps understand where its true seed resides.
Coconut Structure Explained
A coconut’s composition involves several distinct layers. The outermost is the exocarp, a smooth, typically green skin that ripens to yellow-brown. Beneath this lies the mesocarp, a thick, fibrous layer known as coir, which provides protection and aids in water dispersal. These two layers form the husk.
Encased within the husk is the hard, woody endocarp, the “shell” most people recognize. This endocarp is approximately 4 millimeters thick and features three distinct “eyes” or germination pores at one end. Inside this shell, the coconut contains both liquid and solid endosperm. The liquid, known as coconut water, initially fills the cavity. As the fruit matures, cellular layers of solid endosperm, or “coconut meat,” deposit along the inner walls, growing up to 11 millimeters thick.
Locating the Embryo
The white “meat” and liquid “water” within a coconut are not the seed, but the endosperm, a nutritive tissue supporting the developing plant. The true seed is a tiny embryo, a small cylindrical structure, typically measuring around 0.8 centimeters long. This embryo is embedded within the solid endosperm, directly beneath one of the three “eyes” on the endocarp.
Of the three “eyes” on the coconut’s shell, two are typically plugged, while one is functional and softer. This functional pore is where the embryo emerges during germination. Its small size and placement within the endosperm highlight its role as the nascent plant, poised to utilize stored resources.
The Sprouting Process
When conditions are right, the embryo within the coconut begins to grow. It utilizes the endosperm—both coconut water and solid meat—as its primary nourishment. The liquid endosperm contains growth substances crucial for early development.
During germination, the embryo pushes a cotyledonary petiole through the functional “eye” of the endocarp, from which the root (radicle) and shoot (plumule) emerge. Simultaneously, inside the coconut’s central cavity, the cotyledonary blade expands to form a spongy mass known as the haustorium, often called the “coconut apple” or “coconut bread.” This haustorium absorbs the stored liquid and solid endosperm, fueling the young seedling’s growth.