Cecidonia xenophana (Körb.) Triebel & Rambold

Lichenicolous mushroom.

    Thallus whitish forming growths in the form of blisters on the thallus of the host, whitish, chalk white. Apothecia buried in the thallus at first then slightly raised, 0.2-0.5 mm in diameter, flat disc, sometimes with a small umbo in the center, black, margin thick, sometimes with large slits, persistent, black. Spores elliptical, simple, hyaline, 10-13 x 5-7 µm. Numerous pycnidia buried in the thallus, with thick brown walls, visible on the surface only in the form of large brownish or black dots, acicular pycnidiospores, 5.5-8 x 1 µm. Photobiont: Trebouxia. Negative colored chemical reactions (or those of the host). Medulla: I-. Rare parasite of Porpidia, in particular of Porpidia irrigua on whose thallus it develops particularly well.

N.B. Obligatory parasite of Porpidia but can sometimes form thalli, apparently independent, at the end after having destroyed that of the host.