Characterisation of calcium crystals in Abelia spp. using X-ray diffraction and electron microscopy

SummaryThe localisation, chemical composition, and morphology of calcium (Ca) oxalate crystals in the leaves and stems of Abelia mosanensis and of A. × grandiflora were analysed using a variable pressure-scanning electron microscope (VP-SEM) equipped with an X-ray diffraction system, a low temperature SEM (LT-SEM), and a transmission electron microscope (TEM). Foliar analyses of macro- and micro-elements were performed on the leaves and stems of A. mosanensis. A greater number of Ca oxalate crystals were observed in A. mosanensis than in A. × grandiflora. Three morphologically distinguishable types of crystals were observed: the prismatic crystals found inside the chloroplast, multifaceted star-like spherical and bladed aggregate crystals (druses) inside the vacuoles of the mesophyll cells, and small angular crystals (sand crystals) inside the cuticle. Semi-solid crystals that may drip and accumulate to become a solid Ca oxalate crystal were observed by LT-SEM, which indicated the growth of druses of Ca o...