Mollisioid fungi, represented by Mollisia (Fr.) P. Karst., are characterized by soft, sessile apothecia with globose, dark-celled excipula, hyaline ascospores, and worldwide distribution in temperate regions. Their generic and species delimitation is difficult due to the lack of distinct features, and studies based on DNA sequences are urgently required. Two genera of mollisioid fungi, Belonopsis and Trichobelonium, comprise relatively few species and are recognized by (0–)1–3-septate ascospores, medullary excipulum composed of loosely interwoven hyphae, and calcium oxalate crystals in the excipulum. Specimens of undescribed species that are morphologically assignable to Belonopsis or Trichobelonium were collected from various sites in Japan and their assignment to the proper genera was attempted. According to a molecular phylogenetic analysis involving members of Mollisiaceae based on concatenated sequences of ITS, LSU, and RPB1, eight taxonomic entities were placed in a strongly supported single clade with Mollisia diesbachiana, separated from the type species of Belonopsis, B. excelsior. A new genus Neobelonopsis was thus proposed to accommodate the undescribed species. In this study, eight new species of Neobelonopsis and two new species of Trichobelonium were described. A new combination was also proposed for M. diesbachiana. The generic distinction of Neobelonopsis and Trichobelonium was supported by molecular analysis. Some additional characteristics to delimit Trichobelonium were identified, such as the presence of anchoring hyphae between the base of the apothecium and subiculum, and the production of abundant crystals and soluble pigments on the colonies. Derivative species of Neobelonopsis were found to have multi-septa in ascospores.
