Morphology and phylogeny reveal two new species and host records of hyphomycetous fungi on species from marine habitats in Thailand.

The marine ecosystem is the largest on Earth, supporting a wide variety of organisms. Fungi in this environment are diverse and play promising ecological roles. This study investigated fungi on submerged, decaying plant materials of species trapped between rocks in seawater in Prachuap Khiri Khan Province, Thailand. Morphological and multi-gene phylogenetic analysis (LSU-ITS-2-SSU for , ITS-LSU-2-2 for , LSU-ITS-1-α-2 for and LSU-ITS- for ) revealed two new species: , characterized by the presence of a hilum and elongating appendages, and , distinguished by a brown to black conidial-like structure composed of interwoven, irregular cells without distinct conidiophores produced in sterile conditions, unlike other asexual morphs. Additionally, two new host records ( and ) are documented, with detailed descriptions of their and morphologies. Detailed morphological descriptions and illustrations are provided. This study contributes to the understanding of fungal diversity in marine environments.