Cerro Machín is located in the municipality of Ibagué. It is a volcano with active fumaroles reaching 2650 m of elevation. Montane forest relics mostly cover it, but the forest in the surroundings has been largely replaced by pastureland. We surveyed its lichenized fungi communities focusing on species composition, community structure, diversity, and phorophyte preferences. Thirty-five of the 113 species observed are new reports for the department of Tolima and six of them for Colombia. The overall species richness is the highest reported in the municipality of Ibagué. In the study area, the forest has a good conservation status indicated by the presence of the genus Sticta. We registered an average of seven lichenized fungal species per tree, i.e., a low richness, possibly due to the exhausts of the fumaroles. A beta diversity analysis showed a high percentage of rare species. We found evidence of some preference of lichens for bark characteristics, but we did not observe specificity towards tree species.