Lecidella elaeochroma (Ach.) M. Choisy
Thallus crustose, often mosaic-forming, thin, rather smooth to slightly uneven, minutely pleated and rumpled, cracked according to the type of bark substratum, rather glossy, pale grey-whitish to yellow-grey or grey-brownish with green tinges when dry, more celadon, grey-greenish to yellow-greenish in shade or when moist, prothallus conspicuous, black (sometimes absent or incomplete in isolated thallus). Apothecia abundant and scattered all over the thallus, 0.5-1 mm diam., disc at first plane, later convex, blackish, black with red tinges when young and moist, blackish when dry and mature, true exciple thin but delimited at first, black, persistent on flat discs, flexuose and finally excluded in convex discs. Ascospores simple, colourless, ellipsoid, 10-17 x 6-9 µm. Photobiont: chlorococcoid. C+ orange or sometines C- (see N.B.), K- or K+ pale yellow, KC+ pale yellow, Pd-, UV+ orange, K/UV+ mint ice-cream green. Abundant, forming large mosaics through confluence of conspecific colonies, on smooth bark of deciduous trees, near the seashore, frequent on Prunus spinosa.
N.B. The reaction to C is variable and capricious and not homogeneous: it can be C+ orange on a thallus of a mosaic and C- on a neighboring thallus of the same mosaic! It can even be C+ or C- depending on the tested area of ​​the same thallus!
_ Amandinea punctata is rather similar but rarer, with chemical spot tests negative, black prothallus absent (however, isolated specimen of Lecidella elaeochroma with a questionable prothallus and C-require ascospores observations to be distinguished from thed 1-septate spored Amandinea punctata.
_ A more frequent morph distributed along the seashore has been described: Lecidella elaeochroma forma soralifera (Erichsen) D. Hawksw. that is green-yellowish and has soralia, 0.5-1 mm on its thallus.
The following chemoforms are sometimes separated (but there are intermediate forms!):
Lecidea elaeochroma chemo elaeochroma: thallus not yellow, C + orange, K- to K + yellowish, KC + orange. Very common taxon.
Lecidea elaeochroma chemo euphorea: thallus not yellow, C-, K + yellow, KC-.
Lecidea elaeochroma chemo flavicans: thallus rich in xanthones, yellow to yellowish. C + orange, K + yellow, KC + yellow to orange. Slightly thermophilic Atlantic taxon.
N.B. Traponora varians is a very similar species that shares the same habitat and sometimes occurs mixted, it is distinguished by a less smooth thallus, slightly convex apothecia without a persistent edge, orange-brown not turning black and smaller spores.
