Description: Defined as non-yellow species of Rhizocarpon with colourless, one-septate spores, the R. hochstetterii group includes over 10 Irish species of which R. hochstetterii is only one. Crustose and upland in distribution and siliceous in its rock preference it has a grey to red-brown cracked thallus a few centimetres across at most, crammed with small angular discs (0.6-1.0mm diam.). All spot tests are negative. Spores are relatively large (>21µm long) compared with lookalikes. Widely but thinly scattered in Ireland.

Key Identification Features:

• Grey to red-brown crust with abundant discs; spores one-septate, large, all reactions negative
• Most frequently confused with R. polycarpon which has the medulla bluing with iodine and epithecium (top layer of disc) K+ purple.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Rhizocarpon hochstetteri at iNaturalist World Species Observations database.