Fusarium species exhibit diverse lifestyles, being commonly encountered as saprotrophs and endophytes, but can also act as pathogens to plants, animals, including humans, and even other fungi. Very little is known, however, about the species diversity of fungicolous Fusarium species. The following study thus aimed to characterize species of Fusarium and related genera associated with smut fungi and mushrooms in Iran by applying a polyphasic approach involving culture characteristics, morphology, and multigene phylogenetic analyses. Twenty-four fungicolous isolates were recovered from different host species spanning four host families in the Eastern Azerbaijan provinces of north and northwest Iran. Isolates belonged to four Fusarium species complexes (SC) in, i.e., F. fujikuroi SC, F. oxysporum SC, F. incarnatum-equiseti SC, and F. tricinctum SC. One other fungicolous taxon was identified as Neocosmospora metavorans. Two new lineages belonging to the F. tricinctum SC are here described as F. gamsii and F. iranicum, both species occurring on Agaricus bisporus. Fusarium gamsii is phylogenetically related to F. torulosum, and F. iranicum to F. flocciferum. Morphological characters support their distinction from their closest phylogenetic sister species. Additionally, A. bisporus and Boletus sp. are here listed as new host records for members of the F. tricinctum SC in Iran.