Dirina fallax De Not. forma fallax Taxon Atlantique

    Thallus crustose, 5-10 cm diam., possibly much more in case of conspecific mosaics, 0.5-3 mm thick, surface uneven, cracked, rough to verrucose, sometimes with blisters or excrescences, pruinose, pale greyish, pale brown-greyish, dull whitish, ochraceous on iron-rich substrata, typically with purple tinge, medulla whitish, prothallus brownish, growth zones visible on isolated specimen, typically thick and swollen, scarred in case of mosaics with a wavy ridge at the junction. Apothecia sessile, 0.5-3 mm diam., disc surface rough, greyish to dark grey or concolourous to the thallus, markedly powdery, whitish to greyish exciple thick, often wavy to distorted, concolourous to the thallus. Ascospores colourless, narrowly ellipsoid, 3-8-septate, 20-24 x 4-6 µm. Photobiont: Trentepohlia, visible as orange spots in eroded sections or around apothecia. Cortex and exciple: C+ red, K-, KC+ red, Pd-; medulla: C-, K-, KC-, Pd-. Rare, on sheltered overhangs of more or less calcareous rocks of seashore cliffs. This species has recently been separated from Dirina massilensis forma massiliensis and Dirina massiliensis forma massiliensis ss. str. which are more whitish Mediterranean species and which come on calcareous substrates. This fertile form of Dirina fallax is very rare in our prospection area where it is replaced by Dirina fallax forme sorédiée and Dirina fallax forme pycnidiée. See Dirina fallax forma fallax Taxon méditerranéen.

For more details see : TEHLER A., ERTZ D., IRESTEDT M. The genus Dirina (Roccellaceae, Arthoniales) revisited. The Lichenologist. 45(4); 427-476 (2013).