Dictyomeridium tasmanicum sp. nov. (Trypetheliaceae) is described from the bark of coastal Allocasuarina verticillata in south-eastern Tasmania. The new lichen has a thin, UV–, epiphloeodal thallus, small but prominent, pleurothelioid ascomata with eccentric to lateral ostioles, and bisporous asci containing comparatively large, muriform-euseptate ascospores