The new lichenicolous fungus, Abrothallus halei sp. nov., is described. The species is characterized by having 4-celled ascospores with a strongly constricted median septum, which split into two 2-celled part-spores, even when still inside the ascus. This is the first Abrothallus known from the genus Lobaria, and the species is reported from Norway and the USA, occurring on L. quercizans and L. pulmonaria.