Sensu stricto, often shortened to s.s. or s. str., means “in the strict sense”. Psilocybe sensu stricto is the genus as redrawn after DNA work: the bluing species, which a 2022 study put at about 165 (Bradshaw et al., 2022). Psilocybe sensu lato, “in the broad sense”, is the older, larger grouping that also held the non-bluing species, put at 277 to 326 species in the same paper.
The split followed a 2007 proposal, led by Scott Redhead of Agriculture and Agri-Food Canada in Ottawa, to conserve the name Psilocybe with Psilocybe semilanceata as its type (Norvell, 2009; Norvell et al., 2010). Gastón Guzmán summed up the outcome in 2012: bluing species stay in Psilocybe s.s., non-bluing ones go to Deconica (Guzmán, 2012).
The labels matter when reading counts. A 2022 review estimated that 52 species which probably belong in Deconica were still filed under Psilocybe (Bradshaw et al., 2022). Some exceptions sit inside the strict genus: a 2026 preprint, not yet peer reviewed, found no psilocybin genes in the non-bluing Psilocybe fuscofulva (Slot et al., 2026).
Sources
- Bradshaw et al., 2022, Applied and Environmental Microbiology
- Norvell, 2009, Mycotaxon 110
- Guzmán, 2012, Acta Botanica Mexicana 100
- Slot et al., 2026, bioRxiv preprint
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