Eight lichenicolous species of Arthonia from Tasmania are treated. Two are described as new: A. aurantia Kantvilas & Motiej., which infects the thallus of a Leprocaulon-like lichen and is characterised by vivid orange, K+ magenta ascomata, 0.07−0.1(−0.15) mm wide, and 1-septate, macrocephalic ascospores, 10−12.5(−13.5) × 4−5.5 µm; and A. endocarpa Kantvilas & Motiej., which infects the apothecia of Amandinea neoconglomerata Elix, and has non-amyloid asci interspersed with those of the host, and is characterised by 1-septate, macrocephalic ascospores, 8.5−13 × 4.5−6 µm. Two other species, A. epiphyscia Nyl. and A. stictaria Nyl., are here recorded for Tasmania for the first time. Salient features of all species are compared. Arthoniaceae, lichens, parasymbionts, taxonomy, Australia