Phacopsis australis

Phacopsis australis grows superficially (i.e., on the surface) on the thallus of its host. Unlike other members of the genus Phacopsis, it is cecidogenous, meaning it does not cause the formation of galls in the host. Its apothecia are dark brown to black, range from sessile to slightly immersed in the thallus, and measure 0.2–0.4 mm in diameter. The hypothecium (the tissue in the apothecium immediately below the subhymenium) is hyaline (colourless) to pale brown, measuring about 20–60 μm thick. The ascospores are ellipsoid to fusiform (spindle-shaped) and contain oil droplets; they typically measure 12–15 by 5.5–7 μm with a 0.5 μm-thick spore wall.^[1]

Known hosts for Phacopsis australis are all from the genus Xanthoparmelia: X. annexa, X. molybdiza, X. conspersa and X. incerta.^[1]

Lecanora lasalliae is quite similar in appearance to Phacopsis australis, but this lookalike lacks algae in its excipulum (the rim of tissue around the apothecia), and has larger ascospores.^[2]

Phacopsis australis is only known from a few collections, in Cape Province and in the Drakensberg region of KwaZulu-Natal. Although one of its hosts, X. conspersa, has a cosmopolitan distribution with many specimens having been studied, the fungus has not been recorded occurring out of South Africa.^[1]