The species was described in 2009 in the journal Mycotaxon by Australian mycologists Genevieve Gates, Bryony M. Horton, and Dutch Entoloma authority Machiel Noordeloos.

The specific epithet refers to not only the type locality, but also the 19th-century indigenous Australian girl Mathinna, after whom the town is named.

The northeastern site is a rainforest located at an altitude of about 850 metres (2,790 ft), containing predominantly trees of the species Eucalyptus delegatensis with an understorey of the shrub Leptospermum lanigerum.

The southwestern site, a low-altitude wet sclerophyll forest, has the trees Eucalyptus obliqua and an understorey of Leptospermum scoparium and Melaleuca squarrosa.

Although it is not known whether the fungus has any specific association with these plants, some Entoloma species are suspected of being mycorrhizal, and members of the Myrtaceae are known to form ectomycorrhizas with fungi.