Dirina massiliensis Durieu & Mont. forma massiliensis Taxon méditerranéen des rochers calcaires abrités.

    Thallus crustose, tightly appressed on its substrate, 1-3 mm thick, moderately smooth to coarsely verrucose, white-greyish, greyish, dark grey, brownish often soiled by a greyish-brown to blackish-brown deposit (cyanobacteria?) or parasitized, prothallus bulging or spreading, sometimes with a pale grey to pale brown zonation. Apothecia sessile, bud-shaped, 1-3 mm diam., disc greyish, minutely rugose, most often hidden by a whitish layer of crystals, exciple very thick, paler than the thallus. Ascospores colourless, 3-septate, narrowly ellipsoid with a rounded end, 20-24 x 4-6 µm. Photobiont : Trentepohlia (thallus scratching induces a yellow mark). Cortex : C+ fleeting pink, K-, KC+ pink to fleeting red, Pd-; medulla: C-, K-, KC-, Pd-. Mediterranean, on sheltered, rather little-lit humid calcareous walls near the seashore. To be compared to Dirina massiliensis forma massiliensis Taxon méditerranéen des rochers calcaires. which is markedly more whitish and grows on dry and well-lit calcareous rocks near the seashore, and may be a different morph without cyanobacteria at the thallus surface. See also Dirina massiliensis forma massiliensis Taxon méditerranéen des murs calcaires that grows on sheltered walls of inland buildings.

N.B. All these forms seem to be connected by intermediaries.