Snyman, H. A. ., H. J. . Fouché, P. L. . Avenant, and C. . Ratsele. “Frost Sensitivity of Opuntia Ficus-Indica and O. Robusta in a Semiarid Climate of South Africa”. Journal of the Professional Association for Cactus Development, vol. 9, Apr. 2007, pp. 1-21, doi:10.56890/jpacd.v9i.237.