Arthonia atlantica
Thallus effuse (spread out and flattened) or forming mosaics with other lichens. White to pale grey, matt, cracked-areolate (crazy-paving like). Apothecia more or less immersed in the thallus, irregulalry rounded (to 0.2mm dia) though more usually elongate or stellate, often joining to form an irregular reticulum (network).
Hard acid rocks in dry underhangs and sheltered sides of old walls, usually near the coast.
SW England, W Scotland, W Ireland and W Wales. Outside the British Isles known only from Brittany.
Records from Wales:
| Location | Grid Reference | Last Rec'd | Recorder | SSSI |
| Cardigan: Codmor NNR | SN14, SN24 | 1996 | A. Orange & P. Wolseley | Yes |
| Caernarfon: Nantgwynant | SH65 | 1973 | A. Pentecost | Yes |
| Meirionydd: Porthmadog | SH58274107 | 2002 | A. Orange | |
| Pembroke: Skomer Island - North Castle | SM7305 | 1750-1996 | Unknown | Yes |
| Radnor: Coed Aberedw | SO0747 | 1960 | Unknown | Yes |
Skomer Island - surveyed by Natural History Museum lichenologists in the mid-1990s, but this species not recorded.
Coed Aberedw - the record in the Welsh Threatened Lichen database puts this site in Ceredigion. But there is no site of this name in this vc and the grid-ref places the record in the Radnor site. This inland site is anomalous however.
Coedmor - occasional on rock outcrops in NNR compartments 2,6,9,10 and 11.
Porthmadog - Pen y Garn, Prenteg. On rocks below overhang in Quercus petraea woodland.
| UKBAP Signposting Actions: | |
| 1. | Monitor the habitat and species at two extant sites, at least every 6 years, to ensure that management maintains or expands woodland continuity and modify accordingly. Pay special attention to threats from excessive shade cast by climbers, and evergreen trees and shrubs, particularly invasive non-native species, and inappropriate grazing levels and forestry operations. |
| 2. | Promote agri-environment schemes capable of delivering appropriate site management. |