Description: This crustose, ‘scripture’ lichen has a green-grey thallus with clustered, often interlocking slit-like discs (lirellae). It is notoriously rare in Ireland. It has been recorded only from yew which effectively is also its main host in southern Britain. It grows along shaded cracks and crevices in the bark of the trunk. All records have been from Killarney, County Kerry. Under the microscope the spores will be seen to be 8- to 14-septate.

Key Identification Features:

• The combination of grey-green (never brown) thallus, yew tree host and 8- to 14-septate spores is diagnostic
• It should be searched for in all areas where yew is planted as a single tree, including botanic gardens.

Original text submitted by Vince J. Giavarini

Distribution Map from NBN: Zwackhia prosodea at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Zwackhia prosodea at iNaturalist World Species Observations database.