Heterodermia leucomela (L.) Poelt

   Thallus in small bush 5 to 15 cm across formed of loose lobes cut into strips 2 to 3 mm wide, more or less divided, curved and straightened. These strips are whitish on both sides, a little powdery on the underside with sometimes soredia, especially towards the margin and lined with numerous characteristic fine cilia, black to blackish, up to 1 cm long. Apothecia not observed. Photobiont: chlorococcoid. C-, K yellow then red, KC yellow then red, C -, P yellow. An emblematic and heritage species, very rare and in decline, occurring in the mossy cracks of the rocks of the maritime cliffs of the temperate zones, from the xeric supralittoral zone to the near aerohaline zone. Much rarer in the oceanic zone in the branches of the canopy at the top of old deciduous trees (but perhaps relative rarity because can hardly be observed except when these trees or their branches are cut or fell) see Heterodermia leucomela forme de la canopée; see also Heterodermia leucomela forme ramicole des arbres à feuilles persistantes coming on evergreen trees (Abies, Pseudotsuga, ..).

NB In Finistère, many stations of this species where it was possible to find beautiful tufts have now disappeared, or are reduced to a few small stunted lobes, the herbarium specimens presented here are an example, the former sample station currently being practically destroyed. (Do not sample).