A corticolous species, Anisomeridium flavovulcanus, is described. It has so far been found in the Carribean and Pacific lowland rainforests of Costa Rica, where it is a frequent lichen in the understorey. This conspicuous lichen is characterized by large conical conidiomata, which release a yellow conidial mass at the apex. Dimorphic conidia occur in the same conidiomata: 1-septate microconidia and thick walled globose macroconidia. Ascomata were found only twice; the inconspicuous perithecia are hemispherical, semi-emergent with an apical ostiole, the asci are cylindrical with a cruciform ocular chamber and the ascospores are uniseriately arranged.