Dirina massiliensis Durr. & Mont. forma sorediata (Müll. Arg.) Tehler Taxon atlantique des murs en pierres peu acides ou en ciment.

  Thallus crustose, rather variable according to substrata, rather thick (1-3 mm), smooth or uneven, rimose, verrucose, sometimes cracked, more or less humpy, colour highly variable according to the composition of substrata and exposition, most often whitish, greyish, pale grey beige-pink for specimen in shaded areas, white, whitish, very pale grey-brown for exposed specimen. Medulla chalk-white, prothallus rather thick, sometimes contiguous to  thallus thickening bulge-like in case of mosaic, greyish, brownish, brown-black, sometimes ringed belted. In this sorediata form, the thallus is more or less covered, sometimes markedly, with small, 0.3-0.4 mm diam., punctiform soredia, greyish and with globose, mounds of paler, granular soredia, 0.5-1 mm diam., grey-yellow, grey-brown, on some neutral to weakly alkaline walls soredia are pinkish when immature. Photobiont: Trentepohlia. Thallus cortex: C+ red, this colour being rather long to appear and most important, vanishing soon within 1 to 2 min. (see picture), K-, KC+ red, Pd -; medulla: chemical spot tests negative and notably C-. This form is sterile. Coastal and saxicolous taxon restricted to carbonaceous limestone, notably vertical walls and overhangs and consequently rather rare in our prospection area on this type of rocks. May also grow on slightly calcareous sandstones and schists on old walls of chapels where it is rather common. May also rather frequeltly be found on neutral or weakly acid schists or sandstones, notably on walls of chapels, and on cement, mortar or concrete. Some other morphotypes growing on old siliceous stones alkanized by mortar leaching with pink soredia when young may be found and difficult to distinguish from Llimonea sorediata . N.B. Analysis of the associated lichens species is helpful to characterize the alkaline subtratum and the presence of Protoblastenia rupestris, Caloplaca flavescens, Verrucaria macrostoma, Verrucaria nigrescens, etc. indicates that confusion with Dirina fallax (growing on acid rocks) is highly improbable.  

    This taxon, or Dirina fallax previously not recognized, is often associated with other species and determine the Dirinetalia massiliensis. Near the seashore, the most frequently associated species are  Llimonea sorediata and Lecanographa grumulosa. (the latter is a parasite of almost all the other species of this complex and strongly modifies the thalli aspects. On coastal rocks and even more frequently on chapel walls, the pale and slightly pink specimen  are easily confused with Llimonaea sorediata of which the thallus is smaller, thinner, pinker, and covered with mounds of pink soredia, notably towards the center, prothallus generally markedly black. Llimonaea sorediata also has a C+ red reaction, but the colour is bright, instantaneous and persistent (See this species). Arthonia endlicheri, of which the thallus is slightly pink, is also C+, but has pycnidia, pale brown-pink soralia and a thicker and lumpy thallus. This latter species preferentially grows in, and is limited to, the xeric supralittoral zone or in the aerohaline zone and mostly on siliceous rocks. The fertile  Dirina massiliensis forma massiliensis Taxon méditerranéen des rochers calcaires is maritime and mediterranean, and grows on sheltered rocks near the seashore and taxa collected under this name in Atlantic area would belong to other populations. See Dirina massiliensis forma sorediata Taxon méditerranéen des murs calcaires very similar but more thermophilic, whose also would belong to different populations (strictly (?) on limestone walls).*

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