Lecanora chlarotera s. str.

Thallus continuous, forming neatly delimited patches, smooth to roughened or warty, pale grey or sometimes yellow-grey; prothallus white, sometimes conspicuous in rapidly growing thalli. Apothecia 0.4–0.8 (–1.5) mm diam., sessile, often aggregated; thalline margin well-developed, peristent, entire to irregularly crenulate or slightly warted, the medulla with massive irregular crystal clusters not dissolving in K; disc flat, pale dull brown to rose- or orange- brown, sometimes very dark brown on twigs in the south, not or rarely slightly pruinose; epithecium usually beige to pale brown, with numerous coarse granules which do not extend down below the paraphysis tips and are soluble in K and slowly in N; hymenium 70–95 µm tall; paraphyses 1.5–2 µm diam., unbranched or sparsely branched, apices 2.5–4 µm diam., slightly swollen and yellow-brown, not capitate. Asci 65–80 × 10–15 µm, subcylindrical to elongate-clavate. Ascospores (9–) 11–15 × 6.5–7.5 (–8.5) µm, broadly ellipsoidal. Conidia 10–14 µm long, cylindrical. Thallus C–, K+ yellow, Pd–, UV reflecting mauve-purple or UV+ orange-brown (gangaleoidin chemotype) (atranorin, chlarotera-unknown, ± gangaleoidin with derivatives, ± roccellic acid).

Traditionally considered to be the commonest corticolous member of the L. subfusca group in the region, but Lecanora chlarotera s. lat. was extremely variable and subsequent studies indicated that overlooked taxa were included; the map of Lecanora chlarotera s. lat. should be interpreted with caution.

Much confused with L. hybocarpa s. lat., which has pale brownish crystals that extend down between the paraphyses that dissolve in K but not in N. L. hybocarpa s. lat. appears much more frequent than L. chlarotera in the south and eastern lowlands at least. Many woodland collections named L. chlarotera in the past prove to be L. argentata, which lacks a granular layer above the paraphysis tips. Care should be taken when separating the superficially similar and primarily saxicolous L. campestris; specimens of that species on timber or dust-impregnated bark can be distinguished by the presence of small crystals only in the thalline margin. L. pulicaris differs in the Pd+ red exciple and the red to orange-brown epithecium with fine granules, not soluble in N. A Pd– chemotype of L. pulicaris may occur but seems not to have been recorded in GBI. Lecanora pseudargentata also has has similar granules in the epithecium to L. chlarotera but has typically darker chestnut disks, which often have thin pruina on them which are UV+ blue-grey/mauve, a red-brown epithecium, smaller spores a more constantly UV+ orange-brown thallus.

Specimens with well-developed, irregularly warted thalline margin and coarsely uneven-warted thallus are sometimes called L. rugosella Zahlbr. (1928). Others with dark disks and olive epithecium have been called L. meridionalis H. Magn. (1932). See also L. horiza and Myriolecis populicola. Small-fruited specimens resemble Lecania fuscella.