Cystolith

Cystolith (Gr. "cavity" and "stone") is a botanical term for the inorganic concretions, usually of calcium carbonate, formed in a cellulose matrix in special cells called lithocysts, generally in the leaf of plants of certain families, e.g. Ficus elastica, the Indian rubber plant of the family Moraceae. Plants in the family Urticaceae, also known as Stinging Nettles, also form leaf cystoliths, but only during their later flowering and seed setting stages. Cannabis and other plants in the family Cannabaceae also produce leaf and flower cystoliths.