Cresponea premnea var. saxicola (Leight.) Egea & Torrente
Lecanactis plocina ss. auct. brit.
Thallus smooth, thin, effuse, sometimes evanescent, greyish, beige-greyish, grey-green when moist, prothallus absent or inconspicuous, darker (possibly shared with other contiguous species). Apothecia scattered all over the thallus, at first slightly immersed, then sessile, 1-2 mm diam., disciform, black, thinly grey-green-pruinose at first, true exciple persistent, prominent, ± crenate or scoured, black. Cylindrical spores with pointed ends, sometimes a little curved, 4-5 (6)-septate, 18-25 x 4.5-6.5 µm according to the literature, 20-28 x 5-6 µm (in KOH) according to our measures. Pycnidia mostly arranged in groups, black. Photobiont : Trentepohlia. Chemical spot tests negative. Rather rare, on vertical shaded walls of mossy siliceous rocks in old oceanic forests. N.B. Differs from the much more common variety that grows on well-lit bark of old deciduous trees Cresponea premnea var. premnea, only by the substratum, i.e. rocks.*