Gymnocalycium horstii subsp. horstii
- =Gymnocalycium horstii subsp. megalanthum in Gymnocalycium 21: 800. 2008 syn. sec. Charles 20092
- =Gymnocalycium megalothelon subsp. brasiliense in Gymnocalycium 33: 1363. 2020 syn. sec. Metzing 20213
- 3. Metzing, D. 2021: Revisions of Frailea, Gymnocalycium and various other genera. – In: Korotkova N. & al., Cactaceae at Caryophyllales.org – a dynamic online species-level taxonomic backbone for the family. – Willdenowia 51: 251-270. http://doi.org/10.3372/wi.51.51208