Latin subterraneus ‘underground’ + Latin proliferans ‘proliferating’. For the offsets that remain underground for a long time.
The original spelling subterraneo-proliferans is correctable to subterraneoproliferans under article 60.11 of the International Code of Nomenclature. With 22 letters, subterraneoproliferans is the longest epithet in the cactus family (the shortest is that of Rebutia eos).
Maarten H.J. van der Meer (2023 Dec 06). Discocactus subterraneoproliferans. Dictionary of Cactus Names. Retrieved from https://www.cactusnames.org/discocactus-subterraneoproliferans