Pecans are the fruit of the hickory tree Carya illinoinensis, a native of North America. While the edible part is commonly called a “seed,” botanically, the entire structure that falls from the tree is considered a drupaceous fruit. This fruit is composed of several protective layers that must be shed or broken to access the rich, edible portion.
The Outer Protective Shuck
The pecan fruit first appears encased in a husk known as the shuck, which is analogous to the fleshy outer layer of a peach or plum. Throughout the summer, this shuck is firm, thick, and a vibrant green color, with a smooth to slightly leathery texture. It is a protective layer that contains the developing nut inside.
This outer casing features four distinct ridges that run from the stem to the tip of the fruit. These ridges contain pre-programmed zones of weakness, called abscission zones, which signal the nut’s maturity. When the pecan is fully developed and ready for harvest, the shuck’s color shifts from green to a dark brown or nearly black tone.
The shuck naturally dries and shrinks, causing it to split along the four ridges, opening into four separate segments called valves. This splitting process, known as shuck split, reveals the hard-shelled nut within. The nut then loosens and falls to the ground for harvest.
The Hard Inner Shell
The structure immediately surrounding the kernel is the hard inner shell, which is technically the seed coat that has undergone lignification, a process similar to wood hardening. This shell is the part most people recognize as the pecan in its unshelled form. Its shape is typically oblong or elliptical, often coming to a slight point at one or both ends.
The shell’s surface is smooth but features various natural markings, streaks, or mottled patterns in shades of light to medium brown. These markings are genetic and vary widely among cultivars. Its primary function is to serve as a robust, non-porous barrier protecting the kernel from environmental damage and pests.
Appearance of the Edible Kernel
The edible kernel, which is the true seed, fills the space within the hard shell. It is composed of two symmetrical halves, or cotyledons, connected at the base and separated by a thin, papery membrane. When removed intact, each half is shaped like a convoluted, lobed crescent.
The kernel’s surface is highly textured, featuring numerous fine grooves and ridges that create a distinctive, wrinkled appearance. This texture is a key visual identifier and can vary in depth and complexity depending on the cultivar. Covering the kernel is a very thin, reddish-brown to golden-brown skin known as the testa.
The color of the kernel ranges from light cream or pale tan to a more amber or golden-brown shade, often darkening slightly in the central groove area. Pecan quality is often judged by this coloration, with lighter-colored kernels preferred by consumers. This inner portion is firm and dense, and its full visual characteristics emerge when the nut has properly dried, or cured, after the shuck has split.