Hypogymnia physodes (L.) Nyl. forme corticole

        Thallus foliose, forming rosettes not very adherent to the substrate, more or less regular 5-10 cm in its greatest length, formed of lobes deeply indented, hollow, convex, swollen, 1-3 mm in width, turned up at their apice, apices supporting lip-shaped farinose soralia, greenish-white, upper surface shiny, pale gray, pale bluish-gray, lower surface shiny, dark brown to blackish, more brownish towards the margin, smooth and without rhizines. Apothecia sparse, stipitate, 2-7 mm in diameter, disc brown-red, margin thin and persistent. Spores colorless, simple, very broadly elliptical, 6-9 x 4-5 µm. Pycnidia often numerous on the lobes, in particular towards the margin, in the form of non-protruding blackish dots (beware of Lichenoconium erodens frequent parasite of this very similar species but which is protruding and discolors the thallus on which it also gives large spots brownish to blackish necrosis). Photobiont: chlorococcoid. Cortex: K + yellow; medulla and soralia: C-, K-, KC + yellow then red, P + red-orange, UV purple. Species growing on the mossy bark of trunks and large branches where it is rarely fertile, see other forms below depending on the substrate. N.B. To be distinguished from Hypogymnia tubulosa, P- and with capitate and globular soralia and from Hypogymnia vittata more brownish and P-.