Description: This rare crustose lichen has a scaly grey thallus with a dense white frosting of granular pruina slashed with shallow fissures. It grows in crevices on steeply sloping limestone rock. It is strongly associated with Collema and Leptogium species often intermingling with or overgrowing them, especially when young. In Ireland, the species has been recorded from Counties Clare, Galway, Sligo and Antrim but a re-examination of the collections is essential.

Key Identification Features:

• Grey scaly thallus covered in white granular pruina
• Crevices in steeply sloping limestone.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Thalloidima diffractum at iNaturalist World Species Observations database.