Degelia plumbea (Lightf.) P. Jorg & P. James morpho. plumbea

   Thallus foliose, rather thick and monophyllous, apparently made of intricated lobes, rosette-forming up to 10 cm diam., upper surface showing thin wrinkles and whitish ridges, positioned in a distinctive network, clearly visible at margins, made of broad lobes with ascending apices, soredia and isidia absent, although occasionally ± knob-like lobules may develop toward the center, some large and thick "warts", or some isidioid small warts in the apothecia vicinity, see respectively : Degelia plumbea forme à gros granules isidioides et Degelia plumbea forme à petits granules isidioides ; the thallus upper face is usually pale grey, lead-grey, blue-grey, brown-grey, the lower surface blue-black, prothallus with a blue-black, conspicuous beard-like hypothallus, often visible at the margins as a characteristic hypothallus "mat fringe"-like, appearing dark-blue under the sunlight. Apothecia, lecideine, 0.5-1 mm, usually numerous; disc flat, seldom convex, except if rainy, red to dark brown, brown-orange, margin paler, hyalin, vanishing (When dry, margins may become whitish and suggest lecanorine apothecia, ruled out by a careful observation). Ascus 8-spored, K/I+ blue, with apical cap clearly visible. Ascospores simple, colourless, ellipsoid, perispore absent, 16-25 x 7-11 µm (15-20 x 6-9 µm according to our measurements). Photobiont : Nostoc. Chemical spot tests negative. This species has an oceanic trend and grows on mossy bark of broad-leaved trees in ± open, relict woodlands near the coast, seldom on coastal rocks, sometimes in combination with Nephroma laevigatum that is also an oceanic species (both thalli seem intricated, see Degelia plumbea vs Nephroma laevigatum). N.B. If the thallus is very large, apothecia scarce and black and if it grows on mossy trunks of tall and old trees of hyperoceanic forest, see also Degelia cyanoloma. N.B. This species is sometimes very similar to Pannaria rubiginosa and some specimen, notably young, may be very difficult to distinguish but the latter has lecanorine apothecia, the thallus upper face has no fine network and is Pd+ orange; however many intermediate puzzling specimen seem to exist and are difficult to discriminate without a careful analysis. In moist areas, some isidiate forms occur see: Degelia plumbea  isidiate form, with a Mediterranean distribution and may be confused with Degelia atlantica.*