Lecanora compallens

Thallus to 3 cm diam., immersed, continuous, shiny, usually with glaucous-grey warts 0.1–0.2 mm diam.; medulla below soredia white; soralia initially 0.1–0.3 mm diam., punctiform, soon aggregating into irregular patches, usually covering most of the thallus except for a marginal zone; soredia granular, 15–30 µm diam., in a dense mass, layered and up to 0·4 mm thick, yellow to slightly mint-green, contrasting in colour with the thallus. Apothecia rare, not known from British or Irish material. Thallus C–, Pd–, K–, UV–; soredia C–, Pd–, K+ yellow to yellow-brown, K/UV (wet)–, UV± pale orange (usnic acid, zeorin).

A member of the Lecanora symmicta group according to Guzow-Krzemińska et al. (2017), thus a candidate for segregation into the genus Zeora Fr. (Ivanovich et al., in prep.). Identical in chemistry to L. strobilina but lacking apothecia and with soredia. L. stanislai is very similar and also has identical chemistry, but can be distinguished by sequencing; it tends to have smaller, slightly bluer soredia that form a uniform layer at an earlier stage of development. The very similar L. expallens is normally C+ orange and always K/UV (wet)+ bright green-yellow, while L. barkmaniana has a greyer thallus, yellower soredia and contains atranorin (K+ strongly yellow). Lecanora compallens tends to favour the more exposed sides of trees, in contrast to L. expallens. Populations of L. expallens from a shaded habitats may have xanthone levels undetectable by TLC. Then, the best diagnostic features are at least partially delimited soralia and a thicker grey thallus in L. compallens.