Pecan: A standout among hickories

   There are eleven species of hickory native to North America and yet the pecan is the only member of the Carya genus that has been developed into a commercially viable orchard crop. Ever wonder why?  It's not all about taste. Sure some of the hickories produce bitter kernels, like the bitternut hickory (Carya cordiformis) and the water hickory (Carya aquatica). However, the shagbark hickory (Carya ovata) produces a sweet, oily kernel that has a delightful flavor.

    What makes pecan (Carya illinoinensis) stand out among all the hickories is a unique shell architecture that makes extracting the kernel much easier. To illustrate the major differences in shell characteristics between pecan and a typical hickory nut I'll be using photos of Kanza pecan and Fairbanks shagbark hickory (photos at right).
   

      I used a bandsaw to carefully slice through a pecan and hickory nut to reveal, in cross section, the relationship between kernel and shell (photo at left). The red arrows point to the portion of the nut's shell that protrudes into the dorsal grove of each kernel. Note that this protrusion in the hickory is basically an extension of the hard outer shell. In sharp contrast, the material that protrudes into the dorsal grove of the pecan is composed of loose packing material rather than shell material.
    This major difference in shell structure becomes obvious when cracking each nut. When a pecan is cracked the material inside the dorsal groove breaks free from the outer shell easing the extraction of kernel. When cracking a hickory, the shell's protrusions into the kernel remain firming attached to the outer shell and can trap portions of nut meat inside of shell fragments.
    The yellow arrows, in the photo above, point to the inner wall partition of each nut. Note that this inner wall in the hickory is composed of the same hard material as the outer shell. In pecan, the inner wall is softer packing material similar to the material found inside the dorsal groove. When a pecan is cracked the inner wall breaks free from the outer shell allowing both kernel halves to fall free of the shell. In contrast, the inner wall partition inside a hickory nut is not easily separated from the outer shell wall during the cracking process. Often, when cracking hickory nuts, the inner wall will trap one of the two kernel halves requiring a second crack to fully remove all the kernel.

     There is one more difference between pecans and hickories that makes pecan easier to shell. In the photo at right, the red arrows point to cleft in the kernel of each species. This is the location of a  secondary inner wall partition that runs perpendicular to the main inner wall seen in the cross-section photos above. The secondary inner wall in hickory is quite prominent and extends deeply into the kernel. This secondary wall is also composed of hard outer shell material that can trap kernel fragments inside broken bits of shell during the cracking process. In pecan, this secondary wall is greatly reduced or not present at all. In cracking a pecan, the secondary inner wall partition may appear as a small sliver of packing material lodged in the tip of the kernel. However, this bit of inner shell material usually falls free of the kernel during commercial shelling.