Comparisons of phylogenetic patterns between coevolving symbionts can reveal rich details about the evolutionary history of symbioses. The ancient symbiosis between fungus–growing ants, their fungal cultivars, antibiotic–producing bacteria and cultivar–infecting parasites is dominated by a pattern of parallel coevolution, where the symbionts of each functional group are members of monophyletic groups. However, there is one outstanding exception in the fungus–growing ant system, the unidentified cultivar grown only by ants in the Apterostigma pilosum group. We classify this cultivar in the coral–mushroom family Pterulaceae using phylogenetic reconstructions based on broad taxon sampling, including the first mushroom collected from the garden of an ant species in the A. pilosum group. The domestication of the pterulaceous cultivar is independent from the domestication of the gilled mushrooms cultivated by all other fungus–growing ants. Yet it has the same overall assemblage of coevolved ant–cultivar–parasite–bacterium interactions as the other ant–grown fungal cultivars. This indicates a pattern of convergent coevolution in the fungus–growing ant system, where symbionts with both similar and very different evolutionary histories converge to functionally identical interactions.