Description: This rust-red, crustose lichen is a feature of upland rocks in areas where iron-rich rock has been exposed by quarrying or mining. One has to be careful here, as many lichens turn yellow or orange in the wet (they become oxidized), but R. oederi has a genuine rust-coloured thallus as does Tremolecia atrata, a lookalike. R. oederi forms rather small thalli with black discs <0.6mm diam. Close attention to the discs reveals a ‘gyrose’ structure where the rim of the disc has become folded inside like a disc within a disc, making the shape of an upturned button mushroom. Northern half of Ireland mostly.

Key Identification Features:

• Small, rust-red crusts on mineralized rocks with gyrose discs <6mm diam.
• Tremolecia atrata is larger and often more common but has a smooth, concave disc (to 0.7mm diam.) which instantly distinguishes it.

Original text submitted by Vince J. Giavarini

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

iNaturalist: Haugania oederi at iNaturalist World Species Observations database.