Justification: Melocactus deinacanthus was known from only one location, however many more subpopulations were detected later on. Still, the range is restricted (extent of occurrence 800 km2) and fragmented. There is continuing decline and the species has no protection. Hence, it is listed as Endangered under criterion B1ab(iii,v).
This cactus is known from central-southern Bahia, Brazil, where it appears to have a very limited distribution east of the Rio São Francisco and west of the Chapada Diamantina. It grows at altitudes between 450 and 600 m asl.