Haematomma ochroleucum var. porphyrium (Pers.) J. R. Laundon

    Thallus crustose, up to 10 cm diam., able to cover large surfaces through merging of conspecific colonies, notably on walls, grey-whitish when dry, grey-green with pale blue tinge when moist, leprose or farinose with numerous soredia, prothallus fimbriate, cotonny, sometimes not well delimited, white to whitish. Apothecia usually in small numbers or absent, O.5-2 mm, immersed at first then prominent, red-scarlet, red-orange. Ascospores fusiform, 3-7-septate, 30-60 x 5-7 µm. Pycnidia red, 0.2 mm diam.. Photobiont: trebouxioide. Thallus : C-, K+ pale yellow, Pd+ pale yellow, apothecia : K+ purple. Var. porphyrium grows mostly on walls, notably of old churches; see Haematomma ochroleucum var. ochroleucum that is more yellowish and above all more fertile and grows mainly on rocks. N.B. For sterile forms, not to be confused with  Schismatomma decolorans (although very rare on walls) and with Schismatomma umbrinum of which the prothallus is dark and well developed. N.B. To some authors, these two varieties are only chemotypes.*