A binomial name is the two-word scientific name of a species. The botanical code that also governs fungi calls it a binary combination of a genus name and a single specific epithet (Madrid Code, Art. 23.1). In Psilocybe cubensis, Psilocybe is the genus and cubensis the epithet. The genus takes a capital letter (Art. 20.1); epithets are written in lower case.
Formal citations add the author. Psilocybe cubensis (Earle) Singer means Earle coined the epithet and Singer moved it to Psilocybe. After the first full mention, the genus can be shortened to its initial, as in P. cubensis, but not when two genera share the letter, such as Psilocybe and Panaeolus.
A binomial is only as good as the evidence behind its use: in a 2025 study, 12 of 42 samples had a species by appearance that their DNA did not support (Cohen et al., 2025). Common names and cultivated labels are not binomials and have no formal standing.
Sources
Last checked .