Peltigera didactyla  

Thallus to 5 cm diam., rosette-shaped or consisting of a few coalescing lobes in small groups level with or sunk into the substratum. Lobes small, 0.5-1 cm wide by 1-2 cm long, mouse-ear-shaped (concave) when young, becoming markedly ascending when fertile. Upper surface finely grey-white tomentose especially towards the margins; when young, laminal, rounded or irregular, pale, sorediose patches are present. Soralia to 2.5 mm diam., discrete, later becoming confluent, filled with pale blue-grey to brown, coarsely granular soredia, disappearing with the formation of apothecia. Folioles and schizidia absent. Lower surface with distinct, raised, pale cream or faintly flesh-coloured to ochraceous veins, anastomosing with well-developed interstices. Rhizines simple, downy, or bottlebrush-like, the apices often somewhat brush-shaped. Photobiont cyanobacteria (Nostoc).
Anamorph: Conidiomata pycnidia, rare. Conidia 6-7.5 × 3-4 μm.
Teleomorph: ascomata apothecia, held vertically, ± oblong, saddle-shaped, red-brown or brown, delicately crenulate and denticulate at the margin. Hymenium hyaline. Interascal tissue of unbranched thick-walled paraphyses, the apices hardly swollen and immersed in a reddish brown mucoid epithecial layer. Asci cylindrical, short-stalked, thick-walled and fissitunicate, the apex rounded with a K/I+ blue annulus, 8-spored. Ascospores 40-75 × 3.5-4.5 μm, narrowly fusiform, the ends rounded and sometimes slightly swollen, 3- to 7-septate, hyaline, thin-walled, smooth, without an epispore, gelatinous sheath or appendages.
Chemistry: thallus with low concentrations of gyrophoric acid (C+ red) and methyl gyrophorate has occasionally been recorded in the soralia. No lichen products detected by TLC.