Tiznado-Hernández, M.E., Fortiz-Hernández, J., Ojeda-Contreras, Ángel J. and Rodríguez-Félix, A. 2010. Use of the elliptical mathematical formula to estimate the surface area of cladodes in four varieties of Opuntia ficus-indica. Journal of the Professional Association for Cactus Development. 12, (Apr. 2010), 98–109. DOI:https://doi.org/10.56890/jpacd.v12i.101.