Species of Tympanis are well‐known pathogens in Holarctic forests, but we know lit‐ tle about their relationship to other genera in Tympanidaceae. The genus Myriodiscus, remarkable macroscopically and a possible pathogen on bamboo, has a complicated taxonomic history and has not been conclusively placed phylogenetically. Species of Myriodiscus have been described under two other generic names, Ascotremellopsis and Gelatinomyces, the latter being related to the pathogenic genus Collophorina. There has been no formal synonymy of these three bambusicolous genera or agree‐ ment on their systematic positions. We combine accurate micromorphology and DNA sequence data to show the link between Tympanis and Myriodiscus and reveal previously unrecognized features of the latter. These two genera show a type of ascus development unique in the Leotiomycetes. With this new data, we have re‐ solved past confusions over the identity of these fungi, determined their systematic position and have proposed the proper synonymies for Myriodiscus sparassoides and one new combination (M. conus).