Italian mycologist Pier Andrea Saccardo is best remembered for his monumental Sylloge Fungorum, the first ‘modern’ effort to compile all identified fungi within a single classification scheme. The existing history of mycology is limited and has primarily focused on developments within England, but this article argues that Saccardo and his collaborators on the Sylloge supported a vital transnational expansion of mycological knowledge exchange and played a crucial role in stabilizing the tangled knot of local naming and identification among the world's amateur and professional mycologists. Written in the ‘universal’ scientific language of Latin, the Sylloge served as an early database of fungal knowledge and symbolized a broader unification of mycological inquiry in a moment of expanded scientific correspondence. The article situates this proto-database in broader histories of big data in biology and shows how the Sylloge formed a globalizing foundation for the twentieth century's major collecting and taxonomic advances in mycology.