High-altitude ecosystems in the Andes present diverse extreme environmental conditions, yet the fungal biodiversity associated with crustose lichens remains largely unexplored. This study investigated the culturable fraction of the Endolichenic Fungi (ELF) community associated with the lichen Acarospora schleicheri (Ach.) A. Massal, collected from the Chilean Altiplano. Using culture-dependent techniques, fungal strains were isolated and identified through macro- and micro-morphological characterization combined with molecular phylogenetics of the Internal Transcribed Spacer (ITS) region. To ensure taxonomic robustness, phylogenetic analyses were performed separately for each identified genus. The results revealed a diverse assemblage dominated by the classes Dothideomycetes and Eurotiomycetes, with Cladosporium and Alternaria being the most representative. Remarkably, we report the presence of Monascus sp. and the basidiomycetous yeast Sporobolomyces reniformis within the lichen thallus, representing a novel record for this host as an ELF. The prevalence of pigmented genera suggests that the ELF community in A. schleicheri may possess specific adaptations to withstand high UV radiation and desiccation. These findings expand the known biogeography of lichen-associated fungi and highlight the Andean lichenosphere as a reservoir of stress-tolerant microbial lineages. Keywords Lichens, Acarospora, Endolichenic fungi, Lichenosphere, Chilean Andes, Monascus.