We are becoming increasingly aware of the dazzling diversity of fungi—new taxa are being discovered from poorly sampled habitats and integrative approaches point at (near-)cryptic species in many groups. The class Laboulbeniomycetes, which is composed of three orders (Herpomycetales, Laboulbeniales, Pyxidiophorales), is no exception. However, still, in the orders Herpomycetales and Laboulbeniales, species are predominantly described based on morphology alone. Here, we present a new species of Herpomyces from Argentina parasitic on Periplaneta fuliginosa, the smokybrown cockroach. Herpomyces spegazzinii, sp. nov., is characterized based on morphology and molecular data. Phylogenetic inference based on internal transcribed spacer (ITS, consisting of ITS1-5.8S-ITS2) barcode region supports the status of this fungus as a separate species, sister to the recently described H. shelfordellae.