Parmelia ernstiae

The thallus of Parmelia ernstiae comprises small rounded lobes that rarely overlap each other. In the central parts of the thallus, the lobes are intermixed with isidia. The thallus has a pruinose coating, which helps to distinguish it from P. saxatilis. The lobes of the lookalike Parmelia serrana are larger than those of P. ernstiae, and typically overlap.

Parmelia ernstiae is widely distributed in Europe and has been recorded in Fennoscandia, including Denmark, southern Finland, and southwestern Sweden. It was reported as new to Norway in 2019, the same year it was reported from Belarus. The eastern limits of its distribution extend to Bosnia-Herzegovina, the Czech Republic, and eastern Germany. In 2023, P. ernstiae was reported for the first time from Madeira, an archipelago of Portugal, expanding its known distribution to the Macaronesian region. Parmelia ernstiae typically grows on tree bark, although a single specimen from Denmark has been found growing on rock. The species has been observed on various substrates, including the bark of Picea species and Quercus robur, as well as on rocks in Madeira. It can be found in different habitats, such as forests with Picea species, edges of deciduous forests, and even on roadside trees. The species appears to be adaptable to various environmental conditions, occurring in both forested areas and more open, anthropogenic habitats. Its presence in Madeira suggests that it may have a broader distribution than previously thought, potentially extending to other Atlantic islands or coastal regions with suitable microclimates.