Baker M. A., Butterworth C. A., Geographic distribution and taxonomic circumscription of populations within Coryphantha section Robustispina (Cactaceae), American Journal of Botany, 2013, 100(5):984-997, doi: 10.3732/ajb.1200619
A comparison of stem and flower morphology and ten microsatellite markers in Coryphantha robustispina populations, with C. poselgeriana as a comparison group. The results document geographical variation and support three subspecies in the authors' treatment. The paper includes habitat descriptions and a discussion of taxonomic boundaries.