The genus Echinocactus Link and Otto, subgenus Homalocephala (Britton and Rose) stat. nov

@inproceedings{Ferguson1992TheGE,
  title={The genus Echinocactus Link and Otto, subgenus Homalocephala (Britton and Rose) stat. nov},
  author={Donald J. Ferguson},
  year={1992}
}