Histochemical, spectroscopic, and X-ray diffraction identifications of the two hydration forms of calcium oxalate crystals in three legumes and Begonia

Abstract

Crystals from species of Rhynchosia, Phaseolus, Canavalia, and Begonia were observed in cleared leaves and their specific locations were noted. Crystals were isolated from leaves, purified, verified for shape with scanning electron microscopy, and characterized as calcium monohydrate (whewellite; Rhynchosia, Phaseolus, and Canavalia) or dihydrate (weddellite; Begonia) by X-ray powder diffraction and infrared spectroscopy. A histochemical technique for calcium oxalate localization was applied to the cleared leaves to complement the physical identifications of the crystals. This histochemical localization (using silver nitrate and rubeanic acid) is specific and represents a simple method for in situ identification of calcium oxalate.