Review finds most fungal species-description introductions lack explicit hypotheses

A review of fungal taxonomy publications from 2020 through 2024 found that three quarters of the assessed introductions scored below the authors’ threshold for a relatively complete section, with only one quarter exceeding 50 points out of 100. The review examined how new fungal species hypotheses were framed and supported, particularly in the introductions to single-lineage publications.

The authors began from the scale of fungal diversity: global species richness has been estimated at between 2.2 million and 13.2 million species, and most remain undescribed. They also noted that land-use intensification, habitat destruction and uneven protection of fungal diversity hotspots increase the urgency of documenting species. Their study was a structured review and assessment of publication content, rather than a new sampling or laboratory experiment, so its conclusions apply to the selected genera, publications and scoring criteria rather than all fungal taxonomy.

Using MycoBank, the researchers identified new species described from 2020 through 2024 in six genera. The sample comprised the ectomycorrhizal basidiomycetes Amanita, Cortinarius sensu lato and Russula, and the filamentous ascomycetes Aspergillus, Fusarium and Pestalotiopsis. These genera were selected to represent contrasting ecological strategies, taxonomic practices and publication cultures. The three basidiomycete genera accounted for 591 new species in 219 publications, while the three ascomycete genera accounted for 322 species in 138 publications.

Publications were divided into four formats: online releases, cumulative studies containing multiple unrelated descriptions, single-lineage studies and monographs. Of the 219 basidiomycete publications, 167 were single-lineage studies, whereas 67 of the 138 ascomycete publications used that format. The detailed scoring analysis was restricted to single-lineage publications because their introductions generally address hypotheses and objectives within one taxonomic group.

Many of these introductions did not clearly state why a new species was considered distinct. The review reported that 134 basidiomycete studies, or 80 percent, and 38 ascomycete studies, or 57 percent, did not articulate an explicit species hypothesis and instead emphasized descriptive information. A new species was named directly in the introduction in 24 percent of the basidiomycete publications and 22 percent of the ascomycete publications assessed.

The researchers evaluated each introduction across five categories: phylogenetic placement, closely related species, morphology, ecology and biogeography, and hypothesis and aims. Each category could receive up to 20 points. Phylogenetic placement was generally the most complete element, whereas morphology was the least complete. Introductions often gave broad descriptions of a genus, but they did not consistently explain diagnostic characters, known diversity, ecological differences or the mechanisms that might account for divergence. Geographic information was commonly descriptive and was not consistently connected to a species hypothesis or testable aim.

The analysis suggests that sequence information was prominent in many publications, but the scoring itself does not establish that reliance on molecular data caused the introduction deficiencies. The authors observed that morphology, ecology, biogeography and reproductive evidence were less fully represented and were not always linked to study aims. This pattern matters because a species name in modern systematics functions as a hypothesis about a distinct lineage, and that hypothesis may be evaluated using phylogenetic, morphological, geographic, ecological or reproductive evidence. An integrative or polyphasic approach combines available lines of evidence when delimiting species.

Several species in the dataset were later recognized as junior synonyms. The review did not establish a causal relationship between introduction quality and later synonymization, but it noted that some junior synonyms had appeared in data releases or cumulative publications, while others had been described in single-lineage papers with limited introductions. The authors stated that hypotheses supported by multiple data sources can help authors compare proposed taxa with type specimens and other closely related material, although obtaining loans, securing permission for destructive sampling and consulting scarce specialist expertise can complicate such work.

Based on the review, the authors recommend that introductions provide concise background linked to current literature, define the focal group and its placement, identify close relatives, summarize relevant morphology, and state a specific hypothesis and aims. They advise against announcing the names or number of new species in the introduction and recommend reserving “sp. nov.” for the section in which the nomenclatural act is made, consistent with the International Code of Nomenclature for algae, fungi, and plants. For papers describing more than five species, they suggest organizing the treatment by infrageneric groups where appropriate. They also recommend interpreting sequence similarity alongside morphology, culture-based evidence, ecology or biogeography when available.

The review acknowledges that online and cumulative formats can efficiently document opportunistic discoveries and provide a foundation for later work. Nevertheless, the authors favour single-lineage or comprehensive studies when higher-quality data and systematic comparisons are possible. Their bounded conclusion is that the sampled introductions often resembled summaries or data releases more than hypothesis-driven studies. Clear aims and integration of evidence could improve transparency and species delimitation, but the study did not directly test whether revised introductions would reduce taxonomic errors or improve acceptance rates.

Subject of Research: Structured review of hypothesis framing and completeness in fungal new-species description introductions

Article Title: Should describing a new species be science or data release? Rethinking introductions in fungal taxonomy

Article References: Caboňová, M., Maharachchimbukura, S. S. N., Noffsinger, C. R., Caboň, M., Li, X.-L., Verbeken, A., Stadler, M., Phukhamsakda, C., Marin-Felix, Y., Guzman-Davalos, L., Wijayawardene, N. N., Adamčík, S., & Hyde, K. D. (2026). Should describing a new species be science or data release? Rethinking introductions in fungal taxonomy. IMA Fungus, 17, Article e186895. https://doi.org/10.3897/imafungus.17.186895

Image Credits: AI Generated

DOI: 10.3897/imafungus.17.186895

Keywords: fungal taxonomy, species descriptions, systematics, publication quality, species delimitation, integrative taxonomy, phylogenetics, morphology, research review, Should, describing, species