Pyrena

A pyrena or pyrene (commonly called a "pit" or "stone") is the fruitstone within a drupe or drupelet produced by the ossification of the endocarp or lining of the fruit.

[1] It consists of a hard endocarp tissue surrounding one or more seeds (also called the "kernel").

[2][3] The hardened endocarp which constitutes the pyrene provides a protective physical barrier around the seed, shielding it from pathogens and herbivory.

[5] The hardening of the endocarp of a developing drupe occurs via secondary cell wall formation and lignification.

The biomineralisation of pyrenes during the life of the plant can aid the preservation of fruit remains in archaeological findings.

Diagram of a typical drupe, in this case a peach , illustrating the layers of both the fruit and the seed; the pyrene is the hardened endocarp which encloses the seed