Melanelixia fuliginosa
Thallus 1-5(-10) cm diam., thin, closely appressed centrally but usually free at margins, rosette-forming or irregular. Lobes 1-2.5 mm wide, often with the apices ± upturned, elongate, contiguous or overlapping; margins rounded, crenate or irregularly incised. Upper surface dark brown to almost black, shiny (often glossy, especially towards lobe ends), isidiate. Isidia copious, cylindrical, smooth, often becoming branched-coralloid, leaving a white area when abraded, often obscuring the centre of the thallus. Medulla white, sometimes with orange pigment (K+ purple [rhodophyscin]) especially in the lower part. Lower surface black, with pale brown, simple rhizines.
Anamorph: conidiomata pycnidial, the conidia bacilliform, ± swollen towards each end.
Teleomorph: ascomata apothecia, occasional, to 5 mm diam., often shortly stalked. Disc dark red-brown to almost black, shiny. Thalline exciple often becoming isidiate. Ascospores 10-14 × 5.5-8 μm.
Chemistry: cortex K–, N–; medulla C+ red, K± purple, KC+ red, Pd–, UV– (lecanoric and 5-methoxylecanoric acids, rhodophyscin, unknowns).
A widespread species with its distribution largely mirroring available habitat. Assessed by Woods & Coppins (2012) as of Least Concern.
Differs from Melanelixia glabratula (with which it was once combined at subspecific rank) by its dark brown rather than olive=green thallus, more copious production of isidia, and its largely saxicolous habit.
Widespread and common in the British Isles, especially in the west and north, although less so in central Ireland.
Primarily on siliceous rocks, tiles (slate) and worked stone, pebbles of fixed shingle beaches, and occasionally on acid-barked trees in exposed conditions.