Psilocybe allenii was described as new to science in 2012 by Jan Borovička, Alan Rockefeller, and Peter G. Werner. The original sample was collected in Seattle, Washington. It is noted to be microscopically similar to Psilocybe cyanescens, but lacks the wavy cap margins characteristic of that species. These samples were collected near the coastal dunes, growing from woodchips. Each print is dense with spores, and arrives sealed in a dish.