The Humid Mountain Forests of Mexico (HMFs) harbor high species diversity and are subject to continuous fragmentation and disturbance. We inventoried the epiphytic mosses in forest fragments and on isolated trees located in the Eastern Sierra Madre (Sierra Madre Oriental). We determined the size and canopy openness of 60 trees and recorded the occurrence of epiphytic mosses on trunks. Ninety-three species and five varieties of mosses were detected, distributed among 61 genera and 26 families. Thirty-two moss taxa were strictly epiphytic and 61 were facultative. Eighteen percent (17 species) of all recorded species were rare and only 3% (3 species) were common. Nineteen genera of phorophytes were sampled. Quercus had the highest epiphytic richness. Species richness and epiphytic mosses assemblages differ between forest fragments and isolated trees. Canopy openness and mean host tree height determine the epiphytic moss richness and species assemblages. Our study further underlines the importance of the Mexican HMFs as a reservoir of epiphytic mosses.