Citizen science has successfully contributed lichen records to air pollution assessments and for detecting biodiversity hotspots, while its potential to survey broad lichen distributions and trends in natural ecosystems is less clear. The main issue is whether non-professional observers would be willing to visit remote areas to record inconspicuous organisms. We launched a nationwide citizen science campaign “Ready! Set! Lichen!” in Estonia (Northern Europe) that focused on collecting digital photo-based data on lichen distributions comparatively on live trees in forests versus in cut-over sites. Altogether 1101 trees were surveyed by 362 participants. Of all observations, 86% were acceptable and revealed 86 species plus 33 morphospecies as identified by experts. For a test set of selected 12 common epiphytic species, the campaign expanded their known national distributions on average 13%, independently of their conspicuousness (thallus type). Our results indicated that a mass participation approach of citizen science: (i) can provide significant data to monitoring broad-scale population trends of common forest lichens, but the contributions remained small regarding (ii) the knowledge on rare and sparsely distributed habitat specialists and (iii) ecological factors behind the distributions (due to difficulties in keeping valid sampling design). We conclude that citizen-science projects on inconspicuous highly diverse taxon groups can contribute to conservation research if these projects are specifically designed for feasible goals, and we outline six main areas of application for lichen studies.