Raphide

A raphide (plural: raphides) is a needle-shaped crystal of calcium oxalate monohydrate or calcium carbonate found in plant cells. Raphides are a type of crystal idioblast, meaning they are formed within specialized cells. They commonly occur in bundles within these cells, often called raphide sacs or idioblasts.

These crystals are believed to serve various purposes for the plant, including:

• Defense: Raphides can be forcibly ejected from the plant cell when disturbed, causing irritation and discomfort to herbivores that attempt to eat the plant. The sharp, needle-like shape of the crystals can embed in the mouth and throat of animals, deterring further consumption. This defense mechanism is especially prevalent in members of the Araceae (arum) family.

• Calcium Regulation: Raphides may also function as a store of calcium within the plant. This calcium can be remobilized when needed for various physiological processes.

• Tissue Support: While less commonly cited, the presence of numerous raphides could potentially contribute to the structural support of plant tissues.

The presence, abundance, and morphology of raphides are often used as taxonomic characteristics in plant identification. They are particularly useful in identifying certain plant families and genera. The size and shape of raphides can vary depending on the plant species and even the tissue within the plant.

Raphides can pose a risk to humans and animals. Ingestion or contact with plants containing raphides can cause intense burning and swelling of the mouth, throat, and skin.