Thallus foliose, to 5 cm broad. Lobes rounded, irregular, 2-3 mm wide (to only 1.2 mm in GB material); upper surface smooth, partially finely striate with isidia, dark blue-grey, often brownish, margins undulate with clusters of granulate or coralloid aggregated isidia, usually brown apically. Lower surface similar to upper, but paler, without rhizines or tomentum. Anatomy: thallus heteromerous, 100-125 µm thick; upper and lower cortex dark-coloured, paraplectenchymatous, 10-12 µm thick, small-celled, individual cells 4.5-6.5 µm diam; inner part of unorientated, interwoven hyphae with aggregates of Nostoc cells, individual cells 4-6 µm diam.
Anamorph: not known.
Teleomorph: ascomata apothecia, very rare, known only in an immature state (0.5 mm diam), laminal, shortly pedicellate with distinct pale thalline, often isidiate margin; disc concave, brownish. Thalline margin 25-40 µm thick, proper exciple composed of small thin-walled cells with isodiametric lumina, 20-50 µm thick. Subhymenium I+ blue, to 40 µm thick, of closely compacted, unorientated hyphae. Hymenium 130-150 µm high, I+ blue, paraphyses conglutinated in a gelatinous matrix, ca 2 µm diam, enlarged apically to ca 4.5 µm with external brown pigmentation. Asci clavate, not fully developed, without ripe spores.
Not formally assessed; potentially overlooked for Leptogium lichenoides.
Similar in many respects to Leptogium lichenoides, but with smooth to minutely striate lobes with rounder, undulate and entire margins with clusters of isidia.
In GB&I, recorded from three sites in Wales (Breconshire and Cardiganshire). Distributed throughout maritime areas of SW Sweden and S Norway, also reported from Austria, Czech Republic, France, Belgium, Luxemburg, Portugal and central Spain.
In GB&I, in freshwater seepage areas and on unshaded siliceous rocks in riverine habitats. Apparently confined to coastal areas in Scandinavia, but also reported on Quercus bark in arid zones on Spain.