The chytrid Gaertneriomyces was first delineated based on a distinct constellation of zoospore ultrastructural characters when the new order Spizellomycetales was erected. Later phylogenetic analysis of small ribosomal, large ribosomal and ITS 1-5.8S-ITS2rRNA gene sequences demonstrated that Gaertneriomyces was polyphyletic, with G. tenuis placing in a separate linage from the type of the genus, G. semiglobifer. In this study we characterize 22 strains placing in the Gaertneriomyces clade and revise the genus. Within Gaertneriomyces, a new species (G. palmatus) is described and two new combinations (G. spectabilis, G. californicus) are made. Additionally, detailed ultrastructure of the G. tenuis zoospore is characterized for the first time, distinguishing its zoospores from zoospores of G. semiglobifer and other described members of the Spizellomycetales. Because its zoospore ultrastructure is unique and in molecular phylogeny it stands alone from the other Gaertneriomyces strains, a new genus, Barromyces, is erected for G. tenuis.
