A holotype is the single specimen or illustration that the author of a species name designated as its type in the original publication, or the only one used to prepare it. As long as it exists, it fixes how the name is applied (Madrid Code, Art. 9.1). Duplicates of the same gathering are called isotypes (Art. 9.5).
Holotypes are kept in fungaria and cited by catalogue number. Psilocybe mexicana has its holotype recorded from Oaxaca, Mexico (Species Fungorum). For Psilocybe azurescens, Kew’s record lists a holotype at the University of Washington herbarium (WTU), collected on 21 November 1993 (Species Fungorum).
Types are now being re-read with DNA. A 2024 study sequenced 71 fungarium specimens, 23 of them type specimens, to rebuild the Psilocybe family tree (Bradshaw et al., 2024). A holotype anchors a name. It is not evidence about cultivated material sold or shared under that name, and many older types are too degraded to sequence.
Sources
- Madrid Code (ICN, 2025), Art. 9.1 and 9.5
- Species Fungorum: Psilocybe mexicana record
- Species Fungorum: Psilocybe azurescens record
- Bradshaw et al., 2024, PNAS: Psilocybe phylogenomics
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