ITS sequencing reads the internal transcribed spacer, a short region of ribosomal DNA that mycologists use as a barcode to place a fungus in a species. In a 2025 study of 42 psilocybin-producing samples, the species assigned by appearance differed from the ITS result for 12 of them, one reason the authors cross-checked with DNA (Cohen et al., 2025).
Barcoding has also exposed errors in museum collections. When researchers checked fungarium specimens labelled Psilocybe, they called the names on them “largely unreliable, even at the genus level” outside a few well-known species (Bradshaw et al., 2022).
The method has a clear limit. In the 2025 study, samples labelled Golden Teacher, B+ and PE all matched Psilocybe cubensis with the same 99.73% identity (Cohen et al., 2025). A species-level barcode cannot separate cultivated labels within one species or show lineage. Questions like that need whole-genome work, such as the 2023 comparison of 86 cultivar genomes (McTaggart et al., 2023). Like any DNA test, ITS describes the sample tested, not every mushroom with the same name.
Sources
- Cohen et al., 2025, Scientific Reports (PMC)
- Bradshaw et al., 2022, Applied and Environmental Microbiology
- McTaggart et al., 2023, Current Biology
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