Agonimia gargominyi (Verrucariaceae, Verrucariales) is described and illustrated from bark samples collected from Morane atoll (Tuāmotu-Gambier Islands, French Polynesia). It is characterized by the large superficial perithecia having a pale brown-colored ostiolar region, the 8-spored asci, and the relatively large lobed squamules. Micromorphology of the ascomata and the thalline squamules matches the genus Agonimia. Additionally, to accommodate the inclusion of this newly identified species, the existing comprehensive key encompassing all known Agonimia species worldwide has been modified and updated accordingly. Detailed illustrations supplement the description of Agonimia gargominyi. Key words: coral reefs, corticolous, lichen, Low Islands, Pacific Ocean, tropics.