Xeromyces is a monotypic genus of fungus in the family Monascaceae.

[2] It is a xerophile, being able to germinate at a water activity levels between 0.62 and 0.97,[5] lower than any other known organism with the exception of Aspergillus penicillioides.

[6] However, it requires a higher water activity level to produce spores.

[7] The estimated genome size of X. bisporus is 24.8 Mb and the fungus lacks the genes normally associated with mycotoxin production.

Its simple asexual state consists of one or two round terminal chlamydospores.