Tremella macrobasidiata is a proposed new species for a lichenicolous heterobasidomycete strictly parasitizing the hymenium of Lecanora chlarotera. It is reported from Spain, and is characterized by large and particularly variable basidia, rather large basidiospores and the production of asteroconidia, forming brownish to dark green galls in the specific host apothecia. The presence of asteroconidia is discussed. Comparisons with closely related lichenicolous Tremella species are also provided.