Realini M. F., González G. E., Font F., Picca P. I., Poggio L., Gottlieb A. M., Phylogenetic relationships in Opuntia (Cactaceae, Opuntioideae) from southern South America, Plant Systematics and Evolution, 2015, 301:1123-1134, doi: 10.1007/s00606-014-1154-1
An analysis of 15 South American species using ISSR markers and two plastid DNA regions. It documents intraspecific variation and the relationships of S. salmiana and S. schickendantzii, named in the genus Opuntia in the paper.