Lecanora expallens

Thallus effuse and granular to rimose, usually forming circular to elongate patches, yellow-green, sometimes with radially orientated crystals evident on the surface; soredia initially arising from discrete, somewhat excavate, lens-shaped soralia 0.1–0.3 mm diam., soon becoming confluent to make a continuous sorediate crust, farinose, pale to lemon yellow; prothallus inconspicuous or when on smooth bark blue-grey. Apothecia when present 0.3–0.8 (–1.5) mm diam., sessile, not constricted below, sometimes angular by compression; thalline margin at first crenulate but becoming excluded, sometimes sorediate; disc pale yellow, pink or brown, flat to slightly convex, sometimes pruinose, matt to waxy; epithecium colourless to pale yellow; hymenium 35–55 µm tall; paraphyses 1.5–2 µm diam., sparsely branched and anastomosed, apices not or slightly thickened. Ascospores 10–16 (–17) × 4–7 (–7.5) µm, broadly ellipsoidal. Thallus C+ deep yellow or orange (? to red), K+ yellow, K/UV (wet)+ bright green-yellow, Pd–, UV+ orange (zeorin, thiophanic and usnic acids, ± arthothelin and ‘expallens unknown’).

A member of the L. symmicta group, thus a candidate for segregation into the genus Zeora Fr (Ivanovich et al., in prep.). When sterile, this species may be confused with Pyrrhospora quernea, which has a somewhat duller, yellow rather than yellow-green or citrine thallus and coarser, nearly isidioid soredia; it also contains arthothelin and not usnic acid. Poorly developed material can be C–, but appears always to show a K/UV (wet)+ bright green-yellow reaction. For comparison with L. compallens and L. stanislai see those species, also L. barkmaniana. L. strobilina is always fertile and is not sorediate.