Irpex lacteus is a common crust fungus distributed throughout temperate areas of the world. It is the type of the genus Irpex. Irpex lacteus is considered a polypore, but depending on growth conditions it can also produce a hydnoid hymenophore. Due to this variability and abundance of the species it has been described as a new species to science numerous times and subsequently has an extensive synonymy. The complete genome sequence of Irpex lacteus was reported in 2017.

Irpex lacteus is a white-rot fungus that inhabits mainly angiosperm branches and trunks. It is one of the most common wood-rotting fungi for instance in urban North America. It is inedible. The fungus has been identified as a cause of pulmonary infections in immuno-compromised humans.

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