Lepra corallina

Thallus rather thick, pure white to pale or dark grey, continuous, rimose-areolate; prothallus often conspicuous, white; isidia 0.1–0.3 mm diam., abundant, often covering the thallus, cylindrical or becoming coralloid, erect or ± decumbent and unoriented. Fertile warts rare, 1.5–2 mm diam., convex, sharply constricted at the base, often with an uneven to warted upper surface enclosing 2-4 (-11) apothecia; apothecial disc 0.3–0.5 mm, ± expanded, flat or ± convex, pale or dark brown, often faintly white- pruinose. Asci 2-spored. Ascospores 80–140 (–230) × 40–80 μm; wall 2–3 μm thick, not zoned or striate. Thallus C–, K+ yellow to yellow-orange, KC+ yellow, Pd+ yellow-red, UV– (thamnolic acid). 

Characterised by the white-grey, isidiate thallus, the isidia being cylindrical-coralloid and without brown apices, and by the presence of thamnolic acid. Pertusaria pseudocorallina has a pale green-grey thallus with a brownish tinge, shorter, ± globose isidia with brown apices and is K+ yellow→red (crystals). P. coccodes is greener grey and also K+ yellow→red (crystals). Thalli commonly support black sporodochial tufts of the lichenicolous hyphomycete Sclerococcum sphaerale, the presence of which suppresses isidial formation in the host.