Phytolith

Phytolith structures

Phytolith from the tree Pittosporum truncatum

Phytolith from the tree Paulownia fargesii

Contrasting phytolith forms found on leaved trees ^[1]
scale bars 20 μm

Phytoliths (from Greek, "plant stone") are rigid, microscopic structures made of silica, found in some plant tissues and persisting after the decay of the plant. These plants take up silica from the soil, whereupon it is deposited within different intracellular and extracellular structures of the plant. Phytoliths come in varying shapes and sizes. Although some use "phytolith" to refer to all mineral secretions by plants, it more commonly refers to siliceous plant remains. In contrast, mineralized calcium secretions in cacti are composed of calcium oxalates.^[2]

The silica is absorbed in the form of monosilicic acid (Si(OH)₄), and is carried by the plant's vascular system to the cell walls, cell lumen, and intercellular spaces. Depending on the plant taxa and soil condition, absorbed silica can range from 0.1% to 10% of the plant's total dry weight. When deposited, the silica replicates the structure of the cells, providing structural support to the plant. Phytoliths strengthen the plant against abiotic stressors such as salt runoff, metal toxicity, and extreme temperatures. Phytoliths can also protect the plant against biotic threats such as insects and fungal diseases.^[3][4]