Arthonia astroidestera Nyl.
Arthonia armoricana Leight.
Arthonia stellaris p.p. auct. brit.
Thallus crustose, to 2-3 cm across, very thin, more or less immersed in bark, cream to cream-yellow, pale greenish, sometimes delimited by a thin prothallus, brownish. Apothecia abundant, 0.5-1 mm across, linear or sinuous, branched or stellate, dark brown, blackish, but seldom seen as such since covered with a thick white pruine, turning waxy when dry and suggesting paraffin wax droplets fallen down from a candle. Ascospores colourless, then brownish, narrowly ovoid, 4-septate, 18-24 x 6-7 µm. C-, K-, KC-, Pd-, and above all, the pruine of apothecia is strongly orange fluorescent under UV light. Rather rare in our prospection area, in shaded locations on smooth bark of deciduous trees (Quercus, Ulex) in humid and dimmer oceanic woodlands.*