Cortinarius erythraeus is a basidiomycete fungus of the genus Cortinarius native to Australia. English botanist Miles Joseph Berkeley described this species as a "blood red" mushroom, "clothed with a thick gelatinous coat" in 1845, from the writings and specimens of James Drummond, from the vicinity of the Swan River Colony in Western Australia. The species name is derived from the Ancient Greek word erythros "red". John Burton Cleland described Cortinarius ruber in 1928 from a collection in Kinchina, South Australia. Later analysis indicated it was the same species as C. erythraeus.