Description: This creamy-white, crustose species only a few centimetres in size occurs frequently on siliceous rocks, including man-made structures. The thallus forms a tight crust with fine cracks across the surface from which powdery soredia arise giving the surface a faintly floury appearance. A dab of C (fresh bleach) will turn it red. The species is scattered in Ireland, and possibly under-recorded.

Key Identification Features:

• The C+ reaction immediately suggests the genus Trapelia
• The creamy colour and slightly greener soredia help to confirm this species.

Original text submitted by Simon Davey

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

iNaturalist: Trapelia placodioides at iNaturalist World Species Observations database.