Lecanactis abietina (Ach.) Körber

    Thallus crustose, thin 10-15 cm across, slightly rugose or leprose, grey-whitish, greyish, pale grey-greenish, occasionally with purple tinge, covered with cylindrical pycnidia, 0.2 mm tall, tips whitish and pruinose. Apothecia rare and often absent, sessile, 1-2 mm diam., disc flat or slightly convex, brown-blackish though seldom visible owing to a thick pruine layer, pale yellow-ochre, exciple thin, persistent, darker. Ascii 8-spored, 75-105 x 12-18 µm. Ascospores narrowly fusiform or acicular, colourless,  (2) 3 ((4)-septate, 30-45 (50) x 3-5 µm according to our measures, 20-40 x 3-6 µm according to literature. Pycnospores banana-shaped, colourless, 15-17 x 2-3 µm according to our measures. Photobiont: Trentepohlia. Thallus and  apothecia : C-, K-, KC-, Pd-, pruine of pycnidia C+ red. On acid bark of trees in relatively dry locations, seldom on coniferous bark in spite of its name). Not to be confused with Lecanactis subabietina of which the thallus is grey-greenish and pycnidia pruine  is C-, K+ yellow, nor with sterile forms of Opegrapha vermicellifera that has smaller pycnidia and is pruine C-, K-. Sometimes parasited by Tylophoron hibernicum, a very similar species in shape to sterile forms of Lecanactis abietina or to specimen with uncomplete apothecia and bright C+ red sporodochia. Tylophoron hibernicum  being a parasite of Lecanactis abietina the two species may be found inextricably mixed.