Description: Thallus crustose, very thin and poorly evident, mostly endosubstratic; soredia yellow, powdery, 0.02-0.05 mm wide, forming discrete, punctiform soralia or later coalescing into a continuous sorediate crust. Apothecia extremely rare, lecanorine, up to 0.75 mm across, with a deep yellow, more or less flat disc and a thin, entire or sorediate margin. Exciple thin to thick, sometimes visible from the outside; epithecium yellow-brown, covered with an epipsamma of minute crystals; hymenium colourless, 55-60 µm high; paraphyses simple, cylindrical or with slightly swollen, up to 3 µm wide apical cells; hypothecium colourless. Asci 16-32-spored, clavate, with an apical dome which is I+ blue only in the internal, lower part, interrupted in the centre by a I+ paler blue strip, Candelaria-type. Ascospores 1-celled to rarely 1-septate, hyaline, oblong to narrowly ellipsoid, 12-15 x 4-5 µm. Spot tests: thallus K- or K+ weakly orange, C- or C+ weakly orange, KC-, P-. Chemistry: calycin, pulvinic acid, and pulvinic acid-dilactone.
Note: on isolated trees, especially in orchards, certainly more widespread in the Alps. This taxon is apparently similar to C. reflexa, but the soredia are farinose, well-delimited, punctiform, and they never develop from a subsquamulose thallus (see Nimis 1993: 193). Both C. efflorescens (with many-spored asci) and C. xanthostigmoides (Müll. Arg.) R.W. Rogers (with 8-spored asci) were reported from Europe: due to the fact that the material is rarely fertile, and that the two species cannot be distinguished when sterile, I provisionally leave under the former name all records from Italy.
Growth form: Crustose
Photobiont: green algae other than Trentepohlia
Reproductive strategy: mainly asexual, by soredia, or soredia-like structures (e.g. blastidia)