A Gymnocalycium that looks extremely well-defended, cloaked all over in thick, rounded spines. The contrast between its plain dark green body and its bold, white spines gives it a cool, striking appearance. Its oldest origin story traces back to German researcher Curt Backeberg, who passed away in 1966. He informally referred to it as a "strong-spined type of G. hybopleurum "—calling it Gymnocalycium hybopleurum var. ferocior, though this was never officially recognized. Because of its unofficial status, it was considered a "nomen invalidum" (invalid name) and grouped under G. monvillei ssp.monvillei , but in 2002 it was reassigned to G. mostii ssp.ferocius )). Then in 2005, based on seed characteristics and other features, it was found to be closer to castellanosii than mostii, and reclassified as Gymnocalycium castellanosii subsp. ferocius. This is the most officially accepted scientific name as of 2026. That said, different websites still use different names, and it's likely that "ferocior" will continue to be used as a sort of nickname. (I have a feeling that part of the reason it hasn't caught on is because "ferocior" isn't actually in the official scientific name. For what it's worth, under botanical naming rules, you can't use "ferocior" in Gymnocalycium—you're supposed to use "ferocius" instead, so technically it was a mistake from the very beginning!).

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