Oxalic acid is an organic acid and the simplest dicarboxylic acid, with the chemical formula H2C2O4. It is a metabolic product in organisms, classified as a moderately strong acid, and is widely distributed in plants, animals, and fungi, where it performs various functions. Research has found that over a hundred types of plants are rich in oxalic acid, particularly spinach, amaranth, beet, purslane, taro, sweet potato, and rhubarb, which contain the highest levels. Since oxalic acid can reduce the bioavailability of mineral elements and easily combines with calcium ions in the human body to form calcium oxalate, leading to kidney stones, it is often regarded as an antagonist to the absorption and utilization of mineral elements. Its anhydride is carbon trioxide.