A new species of lichenicolous fungus from India – Opegrapha acarosporae, colonising the thallus of Acarospora fusca is described from the alpine region of Central Himalaya. The taxon is characterized by warty ascomata bearing 4-spored asci having uniseriately arranged 3-septate hyaline ascospores measuring (15–)18–23(–25) × (5–)7–8(–8.5) µm with a brown granular perispore. Keyword: Acarospora fusca, Arthoniales, Himalaya, new taxon, Opegrapha pulvinata, Opegraphaceae.