Diplotomma chlorophaeum (Hepp. ex Leight) K. P. Singh & S. R. Singh
Thallus crustose, 2-5 cm, white, smooth to slightly humpy, thick and then dull white, or thin and then very pale greyish, minutely cracked-areolate (old earthenware-like), dark prothallus usually absent but in case of large colonies a pale grey prothallus may be observed (N.B. this prothallus is noticeable mainly where the thallus is thin or eroded and represents a reliable identification trait of this species in the field in addition to its habitat). Apothecia leceidine, 0.2-0.6 mm diam., dimly prominent, disc flat, later becoming convex, black, without pruine; thalline exciple torn at first soon disappearing. The thallus and apothecia complex resembles to an enucleated eye. Ascospores brown, broadly ellipsoid, (1-2)-3-septate at first, then to sub-muriform, 15-24 x 10-12 µm according to literature, 15-20 x 9-12 µm according to our measures. Photobiont: chlorococcoid. Cortex: C-, K+ blood-red, KC+/- with red marks, Pd- slightly yellow-orange due to medulla reaction. Medulla: C-, I+ blue, K+ weakly red-orange, KC-, Pd+ weakly yellow-orange (visible under magnification lens). Not frequent, though it may form colonies on sheltered, coastal weakly acid or calcareous rocks, seldom on concrete, at the 'marine' orange Caloplaca level of which this species might be parasitic. Close to Diplotomma alboatrum that is not especially maritime, but the latter differs by its pruinose apothecia and the negative chemical reactions. On more alkaline calcareous rocks in similar habitats Diplotomma glaucoatrum may be found, but this species has negative chemical spot tests. N.B. This species is highly variable and two taxa sharing the same habitat, the same chemical spot test results and ascospores morphology have different thallus aspects: one whitish, thick with scarce apothecia, the second thin, pale grey with numerous apothecia.