Pseudothelomma ocellatum

Pseudothelomma ocellatum is a species of lignicolous (wood-dwelling), crustose lichen in the family Caliciaceae. This lichen is characterised by its grey, areolate thallus that produces abundant lichenised diaspores, such as short spherical isidia and coarse, dark brown-black soredia. It is typically sterile, meaning apothecia (fruiting bodies) are absent.

Pseudothelomma ocellatum is primarily a Northern Hemisphere lichen, especially found in temperate to cool temperate areas, and somewhat rare in North America where its range has expanded from southern California to the Yukon since its first documentation in 1978. Its habitats include weathered wooden structures influenced by nitrate enrichment, and while it is largely found in European mountain ranges and reported in New Zealand and South Africa, recent findings also place it in Tasmania, suggesting a broader distribution than previously thought.

Catillaria fungoides and overgrown Buellia griseovirens share certain visible traits with P. ocellatum, like dark pigmented soralia, but differ in substrate preference and chemical composition, respectively. Cyphelium inquinans also resembles P. ocellatum but is distinguishable by its crust texture, exciple colour, and absence of the sorediate-isidiate feature that characterises P. ocellatum.