The phylum Ascomycota is one of the largest groups of fungi in the kingdom. The recognition of groups has changed with the development of mycology, such as the ultrastructure of sexual or asexual morphs, the whole-life cycle, and molecular phylogeny. This presentation will explain the taxonomic background of the current classification system and the changes in the traditional classification system. One of the challenges in studying the phylum Ascomycota is convergent evolution, a taxonomic and phylogenetic issue that has been discussed. Species diversity has also been the subject of many studies (taxonomists, ecologists, and plant pathologists). In recent years, the existence of “invisible” or “dark” taxa has also been discussed, although its actuality has not been proven. The presenter has encountered similar cases of ongoing research on black yeast and introduced trial and error and the problems that arose in the process. The post-genomic era has arrived, and the circumstances might be changed, although the presenter believe that our basic stance will remain the same: the investigation of newly fungal lineages/fungal systematics are still supported by steady field research, the re-examination of previous studies.