Vargas-Luna M. D., Hernández-Ledesma P., Majure L. C., Puente-Martínez R., Hernández Macías H. M., Bárcenas Luna R. T., Splitting Echinocactus: morphological and molecular evidence support the recognition of Homalocephala as a distinct genus in the Cacteae, PhytoKeys, 2018, 111:31-59, doi: 10.3897/phytokeys.111.26856
A phylogenetic analysis of all species assigned to Echinocactus at the time, based on morphology and chloroplast and nuclear DNA. The authors separate Homalocephala with three species and confirm the position of the former E. grusonii outside Echinocactus proper. They compare stem, seedling, flower, fruit and seed traits. The paper includes new name combinations and identification keys.