Dirina fallax De Not. s.l.

   General description: Thallus crustose relatively thin, 0.2-1.5 mm thick, more or less smooth and cracked and often rough to warty, colorings very variable depending on the substrate and the exposure: gray-brownish, greyish, ochraceous, often with purplish-brown or purplish-gray tones in areas exposed to spray and sun, hypothallus sometimes present, very thin and frayed, rarely zoned, pale ochraceous brown. Apothecia very rare in our prospection region or else aborted, scattered in the center of the thallus, first submerged then warty and finally sessile and tightened at the base, 0.3-1.5 mm in diameter, irregular margin a little wavy, concolorous to the thallus, greyish to dark brown disc, pruinose. Spores colorless, elliptical, 3 or more septate, 18-24 x 5-6 µm. Photobiont: Trentepohlia. Thallus: K-, C + weak and fleeting red, KC + red, P-; apothecia disc: C + red; medulla: C-. Rare species on, or under, the acid rocks at the seaside where this species replaces Dirina massiliensis of rocks or limestone walls for a long time confused, rarer on the walls and then very similar to Dirina massiliensis and in practice indiscernible. The fertile form: Dirina fallax forme fertile is very rare in our prospecting region, because it occurs mainly on the vertical faces, or under the overhangs of acid siliceous rocks in the Mediterranean region; on the other hand, there are two more common forms: the sorediate form: Dirina fallax forme sorédiée whose thallus is sorediate and the pycnidiate form whose thallus is covered with pycnidia: Dirina fallax forme pycnidiée (sometimes we can observe chimeras with part of the thallus pycnidiate and the other sorediate, see photographs!). N.B. Species sometimes parasitized by Syncesia myrticola which can "absorb" it completely before leading an independent existence, see Syncesia myrticola parasite de Dirina fallax..