Cystolith

A Zystolith or cystolith (Greek kystis, bag '; lithos ' stone' ) is a thickening of a plant cell wall in the form of a more or less stalked body containing heavy deposits of calcium carbonate. These small calcium carbonate granules can take different forms. You can reach a diameter of 30 to 70 microns.

Cystoliths occur (Urtica cannabina) or in rubber trees (Ficus elastica ), for example in nettles as stinging nettles (Urtica dioica) and the Siberian hemp nettle.

They are particularly numerous in older leaves. So you should use of stinging nettles or the Siberian hemp nettle only the young leaves and shoots for consumption, since the Cystoliths irritate the kidneys.