Haematomma sorediatum R. W. Rogers

    Thallus crustose, thin, more or less continuous to slightly rimose, pale greyish, dull whitish but often white, prothallus grey-black effuse though clearly visible, covered with minute rounded to punctiform soralia, 0.1-0.5 mm diam., producting flat farinose to granular soredia, pale yellowish. Apothecia very rare, and when present, scarce and uncompletely developed, sessile, 0.2-0.8 mm diam., disc flat, bright scarlet, exciple smooth to weakly sorediate, whitish with large crystals under the microscope. Asci with 8 spores, 70-90 x 25-35 µm according to our measurements. Ascospores very elongated, a little curved with one end attenuated, 9-12 (16) septate, 60-80 x 4-5 µm according to the literature; 8-12-16 septate and 50-70 x 5-6 µm according to our measurements. Simple paraphyses with non-swollen extremities. Photobiont: Trebouxioid. Thallus and soralia : C-, K+ pale yellowish, KC+ yellow, Pd+ pale yellow, apothecia disc : K+ dark purple. Very rare, on more or less smooth bark trees in humid woodlands, sometimes directly on wood, usually near the river banks.

N.B. This species might not be as rare as usually stated. In fact sterile specimen are almost impossible to identify in the field and the fertile specimen are far less common.

N.B. It probably corresponds to the rather common fertile form of Lecanora punicea described during the 19th century in the Finistère by the CROUAN brothers in their Florule du Finistère.