Druse are groups of crystals of calcium oxalate, silicates, or carbonates present in plants. Calcium oxalate (Ca(COO)2, CaOx) crystals are found in algae, angiosperms and gymnosperms in a total of more than 215 families. These plants accumulate oxalate in the range of 3%-80% (w/w) of their dry weight  via a biomineralization process in a variety of shapes. Araceae have numerous druse, multi-crystal druse and needle shaped raphide crystals of CaOx present in the tissue. Druse are also found in leaves and bud scales of Prunus, Roses, Allium, Vitis, Morus and Phaseolus. The poisonous substances in druse are thought to be a defense against herbivory.
How Druse are Formed
A number of biochemical pathways for calcium oxalate biomineralization in plants have been proposed. Among these are the cleavage of isocitrate, the hydrolysis of oxaloacetate, glycolate/glyoxylate oxidation, and/or oxidative cleavage of L-ascorbic acid. The cleavage of ascorbic acid appears to be the most studied pathway. The specific mechanism controlling this process is unclear but it has been suggested that a number of factors influence crystal shape and growth, such as proteins, polysaccharides, and lipids or macromolecular membrane structures. Druse may also have some purpose in calcium regulation.
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