Diversity and taxonomy of endophytic Chaetomiaceae (Sordariales) associated with roots of wild Orchidaceae in Brazil

Fungi in the family Chaetomiaceae are ubiquitous, colonizing diverse substrates and frequently occurring as endophytes in various plant species. Despite their prevalence, knowledge of their association with the Orchidaceae remains limited. In this study, we investigated the diversity of endophytic fungi associated with the roots of wild orchids. Based on comprehensive morphological and multigene phylogenetic analysis (ITS, LSU, tub2 , and rpb2 ), 51 isolates were identified as belonging to six Chaetomiaceae genera: Arcopilus , Chaetomium , Collariella , Dichotomopilus , Humicola , and Pseudohumicola . Among these, 19 isolates represented ten new species, and 32 isolates were identified as belonging to 12 described species: Arcopilus amazonicus , A. aureus , and A. cupreus were recorded, and four new Arcopilus species were described: A. abbreviatus sp. nov ., A. endophyticus sp. nov ., A. kasuyae sp. nov ., and A. singularis sp. nov ., for which a description of the asexual morph is provided, offering new insights into the morphological diversity of the genus. Five Chaetomium species were identified: C. coarctatum , C. cochliodes , C. globosum , C. pseudocochliodes , and C. tenue . Furthermore, Collariella fluminensis sp. nov . and Dichotomopilus brasiliensis sp. nov . were proposed, while D. variostiolatus was reported for the first time as an orchid root endophyte. Three new species of Humicola were discovered: H. capillata sp. nov ., H. paraisoensis sp. nov ., and H. purpurea sp. nov . Furthermore, Pseudohumicola crispata sp. nov . is described, alongside descriptions of the sexual morph of Ps. pulvericola and the acremonium-like synanamorph of Ps. cinnamomeobrunnea . Based on morphological analyses and the genealogical concordance phylogenetic species recognition (GCPSR) we propose the synonymization of A. albae under A. cupreus , and C. albiziae under C. cucumericola . These findings significantly expand the known diversity of Chaetomiaceae and highlight the complex fungal communities associated with wild orchids.