Christian Hendrik Persoon (1761-1836) was a prominent and independent mycologist living in Paris who prepared taxonomic treatments of fungi based on dried specimens. He reached out to a broad network of naturalists to send him specimens to describe. When he saw the name “Chaillet” referenced in Candolle’s Flore Française (1815) he sought out a connection through a mutual acquaintance. Jean-Frédéric Chaillet (1747-1839) in retirement became a fervent local naturalist in Neuchâtel, Switzerland with a broad interest to catalogue the plants, algae, mosses, lichens, and fungi of the region. He documented this through an extensive and meticulously prepared personal herbarium by identifying them himself using his own library or through specialist identifications. Persoon and Chaillet quickly set up a system where over eight years (1816-1823), Chaillet would send specimens of fungi to Persoon with an accompanying list. Persoon would then identify the fungi, annotate the list with identifications and remarks, and send back to Chaillet who could then update his collection. Chaillet would contentedly acknowledge the identifications but sometimes even debate taxonomy and nomenclature, to the point of even discouraging some of Persoon’s proposed new species. Their complete transcribed correspondence demonstrates both the authority and interest of Persoon to ask questions about ecology, morphology, color of the fungi, and to request additional material or color illustrations if needed. Their collaboration led Persoon to name 72 new taxa of fungi from the limestone substrate Jura mountains around Neuchâtel, Switzerland.