Water-filled tree holes (dendrotelmata) are mostly ephemeral micro-ecosystems characterized by high level of heterotrophic microbial activity sustained by allochthonous organic matter. In this paper, description of a five-year long observation of fungal consortia in a Norway maple tree-hole is presented. Overall, 139 fungal taxa were detected. Among them, Excipularia fusispora, Ellisembia leptospora, Rebentischia unicaudata, Tricladium castaneicola, Thielavia terricola and Alternaria spp. occurred most frequently. Our observations suggest that even an individual dendrotelma represents an exceptional microhabitat, forming a hot-spot for microfungi due to its role as a natural spore trap and its (temporarily) aquatic environment. Our results show that this aquatic micro-ecosystem supports highly diverse mycobiota with continuous temporal dynamics, with an important fraction of sporadic taxa.