Xanthoria polycarpa
Thallus <3 cm diam. (often much smaller), of small appressed rosettes of crenulate lobes, orange-yellow to yellow, with grey morphs mostly occurring in shade; forming small orbicular hummocks. Lobes broadening towards the apices, which are finely divided into many tiny lobe-ends <1 mm across; attached by hapters. Soredia and isidia absent. Upper surface with crowded apothecia, often completely covering and obscuring the underlying thallus.
Anamorph: conidiomata pycnidia. Conidia 2-3 μm long, ellipsoidal.
Teleomorph: ascomata apothecia, to 4 mm diam., contorted, erect, peltate, often with short stalks, flat and orbicular when young with prominent raised margins, becoming contorted when old, the thalline exciple sometimes becoming excluded, grey-yellow (grey in shade). Disc brown-orange. Ascospores 11-15 × 6-8 μm.
Assessed by Woods & Coppins (2012) as of Least Concern.
Throughout the British Isles. BLS map here.
Most commonly on the nodes, axils and leaf scars of dead twigs on shrubs with wide-spreading branches, especially Populus spp., Salix spp., Fraxinus, Larix and Sambucus niger, also on a wide variety of tree-twigs, wooden fences and rock outcrops in farmland, and churchyards, where polluted with agricultural nitrogen; common and increasing.