Description: Thallus foliose, heteromerous, dorsiventral, forming up to 10 cm wide, regular rosettes, but often dying in central parts, the lobes closely adnate, up to 1-1.5 mm wide, rounded at apices, contiguous for much of their length, swollen and hollow inside, grey to greenish grey, often brownish at the ends and along margins, smooth and glossy, with round to oval, dark perforations, and whitish, rounded, more or less stalked, convex, not perforate and not marginally proliferating soralia. Lower surface black, wrinkled, erhizinate. Upper cortex paraplectenchymatous, the cell walls with isolichenan; medulla soon becoming hollow, lining the cavity inside the lobes; lower cortex dark, paraplectenchymatous. Apothecia extremely rare, lecanorine. Epithecium brown; hymenium and hypothecium colourless. Asci 2-spored, Lecanora-type. Ascospores 1-celled,hyaline, ellipsoid, 50-70 x 30-36 µm, thick-walled. Photobiont chlorococcoid. Spot tests: upper cortex K+ yellow, medulla K+ yellow, C-, KC-, P+ yellow-orange, UV-. Chemistry: upper cortex with atranorin, medulla with stictic, constictic, menegazziaic acids, and with or without low amounts of norstictic acid.
Note: on bark in humid beech-fir forests, exceptionally reaching the submediterranean belt. It is included in the Italian red list of epiphytic lichens as “Vulnerable” (Nascimbene & al. 2013c). See also note on M. subsimilis.
Growth form: Foliose, broad lobed
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)
Most common in areas with a humid-warm climate (e.g. most of Tyrrenian Italy)