First described in 1934 by Veli Räsänen, it has become a significant model organism in fungal evolution studies due to its specialised host relationships.

Johann Jacob Dillenius first documented what would later be recognised as B. usnearum in his 1742 work "Historia Muscorum" describing small fleshy nodules closely appressed to Usnea branches.

[6] Räsänen formally described Biatoropsis usnearum in 1934, initially classifying it as an ascomycete based on what he interpreted as asci containing hyaline, simple spores measuring 10–16 by 4–6.5 μm.

The true nature of B. usnearum as a heterobasidiomycete was not confirmed until 1990, when detailed microscopic examination revealed a hymenium with auricularioid basidia and no ascomycetous structures.

[10] Three additional species were formally described from this complex in 2016:[11] Research has shown that host switching, rather than cospeciation, has been the primary driver of diversification within this group, particularly in host-specialised lineages.

The anamorph is characterised by its hyphomycetous growth form, producing long branching chains of hyaline, ellipsoid conidia measuring 3–5 by 2–3.5 μm.

The taxonomic understanding of this species was hampered for many years because lichenologists examining infected Usnea specimens generally had limited experience with heterobasidiomycetes, leading to misinterpretation of probasidial structures as asci or spores.

These typical forms can be distinguished from other members of the species complex by this consistent colouration and size, though some specimens may darken due to parasitic fungi.

As the fungus grows upward through the host's cortex, it begins producing reproductive structures, eventually forming a mature gall that lacks algal cells entirely.

The fungus also produces an asexual reproductive form (anamorph) that creates long, branching chains of clear, oval-shaped cells measuring 3–5 by 2–3.5 μm.

[13] While the fungus is most commonly found growing on various species of Usnea lichens worldwide, it has also been documented on the related genus Protousnea.

[14] Biatoropsis usnearum sensu stricto is found growing specifically on six Usnea species: U. subfloridana, U. barbata, U. cavernosa, U. florida, U. glabrescens, and U. intermedia.

The species has been confirmed from several locations in Europe (Austria, Finland, Poland, Sweden, and Scotland) and North America (Alberta and British Columbia in Canada, Minnesota in USA).