A. . Tovar-Puente, M. . Pando-Moreno, H. G.-R. González-Rodríguez, L. . Scott-Morales, and S. de J. . Méndez-Gallegos, “Density of Calcium Oxalate Crystals in 15 Prickly Pear Cultivated Species”, J PROF ASSOC CACTUS, vol. 9, pp. 91–98, Oct. 2007.