Pyrena
A pyrena or pyrene, commonly called a pit or stone, is the fruitstone inside certain types of fruit, namely drupes or drupelets, and consists of a hardened shell-like layer surrounding one or more seeds. It is produced by the ossification of the inner lining tissue of the fruit, called the endocarp. The hardened endocarp which constitutes the pyrene provides a protective physical barrier around the seed, shielding it from pathogens and herbivory.
While many drupes are monopyrenous, containing only one pyrene, pome-type fruit with a hard, stony endocarp are typically polypyrenous drupes, containing multiple pyrenes.
Development
The hardening of the endocarp of a developing drupe occurs via secondary [cell wall] formation and lignification. The biopolymer lignin, also found in wood, provides a structure within secondary cell walls which supports the polymerisation of cellulose and hemicellulose; together these polymers provide the endocarp with tensile strength and stiffness. Further hardening occurs during the biomineralisation of the endocarp. The biomineralisation of pyrenes during the life of the plant can aid the preservation of fruit remains in archaeological findings.
Uses and culture
Pyrenes have been employed worldwide in many cultures for many uses. The stones of some fruits, such as peaches, are sometimes used to infuse flavours into foods and drinks, including peach pit jelly, vinegar, and alcoholic beverages like ratafia. In China, fruitstones are used in a traditional folk handicraft, namely fruit pit carving, to make jewellery and sculptures. Shaivite and Buddhist practitioners use the stones of the fruit of Elaeocarpus ganitrus, called rudraksha, as prayer beads for akshamala.