Three new thermotolerant species of Corynascus isolated from Indian and Argentinian soils are described and illustrated: C. sexualis sp. nov. characterised by small ascospores and the absence of a Myceliophthora anamorph (present in all other species of the genus); C. similis sp. nov. characterised by navicular ascospores with two lateral to sub-terminal germ pores; and C. verrucosus sp. nov. distinguished by the ellipsoid ascospores with two oblique to sub-terminal germ pores. A study to compare the ITS-region sequences of all species of the genus with representative species of related genera demonstrated that this region is very conserved in this group of fungi and of low taxonomic value. A key to the eight species of the genus now known is provided. The molecular data suggest the genus is best placed in the Chaetomiaceae rather than the Ceratostomataceae.