Armillaria mellea
In 1893, the American mycologist Charles Horton Peck reported finding "Armillaria" fruiting bodies that were "aborted", in a similar way to specimens of "Entoloma abortivum". It was not until 1974 that Roy Watling showed that the aborted specimens included cells of both "Armillaria mellea" and "Entoloma abortivum". He thought that the "Armillaria" was parasitizing the "Entoloma", a plausible hypothesis given its pathogenic behaviour. However, a 2001 study by Czederpiltz, Volk and Burdsall showed that the "Entoloma" was in fact the microparasite. The whitish-grey malformed fruit bodies known as carpophoroids were the result of "E. abortivum" hyphae penetrating the "Armillaria" and disrupting its normal development.