Faigón A., Galati B. G., Rosenfeldt S., Kiesling R., Epidermal characters of Pterocactus (Opuntioideae, Cactaceae), Haseltonia, 2011, 16(1):57-66, doi: 10.2985/1070-0048-16.1.57
A microscopic comparison of the epidermis in eight Pterocactus species. It includes descriptions of stomata, papillae on epidermal cells, cuticular sculpture and wax distribution. The authors discuss the value of these traits in distinguishing similar species.