Didymocyrtis slaptoniensis

Areas of Xanthoria parietina infected with this fungus are usually tinged a distinctive reddish colour. Perithecia occurring on host thallus have a raised ring of host tissue around them. Perithecia also occur in the host apothecia. Within the perithecia, brown, two- celled ascospores are arranged in a single line in narrow asci. The ascospores have small warts on their outer walls. Pycnidia with colourless, single- celled spores also occur. The conidia are colourless and single-celled.

Similar species: Pyrenochaeta xanthoriae also forms pycnidia on X. parietina and has colourless, single-celled spores but this species has dark hair-like structures (setae) on the top of its pycnidia.

There appears to be a second form of Didymocyrtis on Xanthoria parietina in the UK. This species is often recorded as Didymocyrtis epiphyscia s. lat. It is only known in its pycnidial form. Spore sizes should be given when making records of Didymocyrtis slaptoniensis.

See Fungi of Great Britain and Ireland &  Ertz et al (2105) Fungal Diversity 74 for key of the genus and description.