Lecanora cenisia Ach.

   Thallus crustose, areolate and a little warty or sometimes bumpy, areoles quite large with irregular edges, whitish, grayish, pale grayish dirty, often with bluish or greenish tones, hypothallus blackish, more or less zoned with blackish blue (or pink if this thallus receives projections of sea water). Apothecia generally numerous, 1-2 mm in diameter, more or less deformed if very numerous, at first barely protruding then sessile and sometimes reduced to an "empty" cup, disc, brownish, grayish, ochraceous, reddish-brown, blackish, margin quite thick, persistent entire to crenate, more or less flexuous, of the color of the thallus. Spores simple, colorless, elliptical, 9-15 x 6-8 µm according to the literature; 13-18 x 5-7 µm according to our measurements. Photobiont: Trebouxia. Thallus: C- (or weak yellow C+), yellow K+ or frequently yellow K+ then blood red, yellow P+ to yellow-orange. Rare species occurring on more or less vertical surfaces of slightly acidic siliceous rocks at the seaside, often with Pertusaria pseudocorallina with which it seems to compete for its algae.

N.B. This species is very variable (sometimes on the same rock!) and the interpretations of this species are numerous and confusing and it seems that it is a collective taxon. We have retained the interpretation of the British authors rather than that of the French authors who consider that this species is mountainous.

Several morphs have been described:

_ Lecanora cenisia morpho atrynea with dark brown, greyish-brown apothecia.

_ Lecanora cenisia morpho melacarpa with blackish, black apothecia.

and it is possible to find on the seaside on iron-rich rocks grey-blue thalli of this species, see: Lecanora cenisia morph avec thalle gris-bleu.

_ In addition there are (to our knowledge!) several species with the same habitat and very similar coloured chemical reactions:

1) Lecanora praepostera with a smooth thallus without large warts or elevations, whitish, ochre cream with a more or less zoned hypothallus and few apothecia often "empty" brown-black to black. Thallus: K+ yellow → red (not blood red), KC +/- red, Pd+ orange-red.

2) Lecanora gangaleoides with a black disk whose epithecium is greenish, the yellow K+ thallus not becoming red, more warty and becoming orange when scratched.

3) Lecanora ochroidea with very sessile apothecia with a brownish and powdery disk and a sinuous and thick margin, pale brownish prothallus a little pink (not black), blood red K+ thallus.

4) Lecanora subcarnea very similar to Lecanora ochroidea but K-.