Powellomycetaceae (Spizellomycetales) contain a diverse group of exogenously developing chytrids found by baiting water preparations of soils and manure with pollen. A previous molecular phylogenetic study indicated that some lineages within this family represent undescribed genera and species. Description of genera within the Spizellomycetales traditionally has relied on ultrastructural characters of zoospores, whereas species have been based on thallus development and morphology. We analyzed Powellomycetaceae chytrids that had not yet had ultrastructural and thallus morphologies determined. Because these chytrids vary little morphologically, we used a linear discriminant function analysis of thallus characters to determine features most useful for separating species when grown in pure culture on identical media. Zoosporic ultrastructures of two groups of isolates differed from those of the two described genera in the family, and we describe the new genera Thoreauomyces with one new species and Fimicolochytrium with two new species. Also, we describe three new species within Geranomyces. Linear discriminant function analysis, although helpful for determining more stable morphological characters, was not completely accurate in assigning chytrids to the correct genus or species, thus emphasizing the importance of molecular characters for identifying these taxa.