The following new taxa are described, based principally on collections from Tasmania: Diploschistes infestans Kantvilas, also present in New Zealand and subantarctic Macquarie Island, a lichenicolous species on Stereocaulon, with (2–)4–6(–8)-spored asci and ellipsoid, muriform ascospores, 26–46 × 12–22 µm, with 5–7(–8) transverse and 1–3 longitudinal septa; Thelotrema oleariae Kantvilas, with 8-spored asci and fusiform, faintly amyloid, grey-brown to brown, sparingly muriform ascospores, 35–78 × 9–15 µm, with 10–15 transverse and 0–1 longitudinal septa; T. pinicola Kantvilas, with generally 8-spored asci and fusiform-ellipsoid, non-amyloid, brown to grey-brown, richly muriform ascospores, 44–130 × 14–30 µm, with c. 20–30 transverse and up to 5 longitudinal septa; T. subdefectum Kantvilas, with (6–)8-spored asci and ellipsoid, faintly amyloid, hyaline, muriform ascospores, 25–46 × 10–20 µm, with 5–8 transverse and 1–3 longitudinal septa; Topeliopsis obscura Kantvilas, with 4–8-spored asci, hyaline, fusiform to narrowly ellipsoid, non-amyloid ascospores, 50–122 × 9–22 µm, with 9–19 transverse septa, and usually containing traces of stictic acid; T. scopulana Kantvilas, a saxicolous species with a relatively thick, well-developed thallus lacking lichen substances, 2-spored asci, and hyaline, richly muriform, ellipsoid, intensely amyloid ascospores, 44–110 × 13–34 µm, with (8–)10–15 transverse and 1–4 longitudinal septa. Identification keys for Thelotrema and Topeliopsis in Tasmania and southern Australia are provided. Ocellularia jugalis Müll.Arg. is a new synonym for Thelotrema bicavatum Nyl. Catillaria stereocaularum (Th.Fr.) H.Oliver, a further parasite on Stereocaulon, is recorded for Australasia (Tasmania) for the first time.