Two new species, Castanediellabrevis and C.monoseptata, are described, illustrated and compared with other Castanediella taxa. Evidence for the new species is provided by morphological comparison and sequence data analyses. Castanediellabrevis can be distinguished from other Castanediella species by the short hyaline conidiophores and fusiform, aseptate hyaline conidia, while C.monoseptata differs from other Castanediella species by its unbranched conidiophores and fusiform, curved, 0–1-sepatate, hyaline conidia. Phylogenetic analysis of combined ITS and LSU sequence data was carried out to determine the phylogenetic placement of the species. A synopsis of hitherto described Castanediella species is provided. In addition, Castanediella is also compared with morphologically similar-looking genera such as Idriella, Idriellopsis, Microdochium, Neoidriella, Paraidriella and Selenodriella.