Toninia mesoidea (Nyl.) Zahlbr.

    Thallus crustose to squamulose-like -not developing on cyanolichens to the contrary of Toninia aromatica- rimose-cracked to areolate, areoles to 0.5 mm with a small squamule aspect, plane, rounded to irregular, sometimes crenulate, brown, brown-olive, grey-greenish when moist, dull whitish when dry, without whitish pruine flocs. Apothecia to 0.8 mm diam., flat then convex, black, exciple excluded when mature. Ascii 50-60 x 15-20 µm according to our measures. Ascospores narrowly ellipsoid, 3-septate, 14-20 x 4-6 µm according to literature, 14-20 x 3,5-5 µm according to our measures. Chemical spot tests negative. Photobiont: Trebouxia. Coastal species, thriving at the same level as Caloplaca marina, Caloplaca thallincola and Hydropunctaria (Verrucaria) maura,  within cracks of neutral to slightly alkaline or acid rocks of the foreshore. It seems to share the same habitat as Verrucaria prominula. Never found on markedly acid rocks like granite or on limestone. Differs from Toninia aromatica by the lack of associated cyanolichens, its coastal habitat in the black and orange zones (though Toninia aromatica may grow on foreshore calcareous rocks), its thallus not truly fragmented nor squamulose, devoid of white pruine, and its smaller apothecia. N.B. Sometimes, it may be difficult to distinguish from 'maritime' specimen of Toninia aromatica in case of growth on slightly calcareous rocks (possible ecotype?).*