Heterodermia leucomela  

Thallus 5-15 cm diam., often in loose rosettes or forming entangled mats, loosely attached. Lobes 0.5-3 mm wide, elongate and ribbon-like, ± parallel-sided, mostly dichotomously branched, entangled, ± ascending with sometimes reflexed apices, with conspicuous long grey to black, simple or sparsely branched marginal cilia 5-9 mm in length. Upper surface ivory-white to pale grey, smooth. Lower surface white, channelled, the central part non-corticate, arachnoid or powdery and then sorediate, the lobes then tending to be broader.
Anamorph: rarely reported; conidiomata pycnidia, with conidia 4-5 x ca 1 µm in size.
Teleomorph: ascomata apothecia, not observed in British material.
Chemistry: medulla C–, K+ yellow→red, KC+ yellow→red, Pd+ yellow (zeorin and salazinic acid).

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