Xylomyces is characterized by the absence of conidiomata, conidiophores, conidiogenous cells, and conidia. The genus only produces chains of large, dark, thick-walled, dry, multiseptate chlamydospores with or without constricted septa. During an investigation of aquatic hyphomycetes
on submerged wood and leaf litter in a stream in the Brazilian Amazon, we found four of the accepted eight species of Xylomyces. Xylomyces acerosisporus, X. aquaticus, and X. foliicola are new records to the Brazilian Amazon, while X. giganteus is a new
record for the southern Amazonian region. Xylomyces giganteus showed the highest relative frequency and occurrence and X. foliicola displayed an intermediate relative frequency and occurrence. Xylomyces acerosisporus and X. aquaticus showed the lowest relative
frequency, while X. acerosisporus indicated the lowest relative occurrence. Descriptions, notes, geographic distributions, and illustrations are presented for all species of Xylomyces found in this study. We also provide a key and a table for all species.