Atmospheric deposition, including airborne microplastics (MPs), poses a growing threat to both natural and urban ecosystems, potentially disrupting ecological balance. Among the organisms affected, lichens are particularly vulnerable, yet their capacity to serve as bioindicators of environmental pollution remains underexplored. This study investigates the bioaccumulation of airborne microplastics in epiphytic lichens across a gradient of anthropogenic pressure. Lichens from the genera Cladonia and Xanthoria were collected at three sites in central Italy: a natural area in Altipiani di Arcinazzo, a protected site within the Castelporziano Presidential Estate, and an urban area in the center of Rome. In total, 90 samples were analyzed to assess both external and internal microplastic entrapment. Samples were digested using hydrogen peroxide and screened for MPs. Recovery rates were calculated to validate the method. A total of 253 microplastic particles were identified, with 97% being fibers and 3% fragments. A clear gradient in microplastic accumulation was observed, increasing from the natural site (n = 58) to the urban site (n = 116). Fiber length was positively correlated with abundance, and the longest fibers were found in the urban site. Additionally, this study reports the first evidence of airborne mesoplastics entrapped in lichens. No significant differences in microplastic retention were found between the two lichen genera. Our findings demonstrate that epiphytic lichens are effective passive biomonitors of airborne microplastic deposition. Their ability to trap both micro- and mesoplastics highlights their potential role in monitoring and possibly mitigating microplastic pollution, especially in sensitive or protected environments. Given their widespread distribution and sensitivity to atmospheric pollutants, lichens offer a valuable tool for environmental surveillance. Their use is strongly encouraged, especially in light of the emerging risks that airborne microplastics pose to both ecosystems and human health.