Smith, G. F., and R. Shtein. “Taxonomic Notes on Kalanchoe porphyrocalyx (Crassulaceae Subfam. Kalanchooideae) and Its Horticultural Derivatives”. Phytotaxa, vol. 478, no. 2, Jan. 2021, pp. 225–238, doi:10.11646/phytotaxa.478.2.4.