Rimularia furvella (Nyl. ex Mudd.) Hertel & Rambold

Lichenicolous lichenized fungus.

    Thallus thick, to 1 mm, rimose-cracked, dark brown to blackish, gradually covering and invading the host thallus  with more or less granular, blackish  isidioid excressences. Apothecia rare, sometimes absent, 0.3-1 mm diam., disc black, exciple thin, concolourous. Ascospores broadly ellipsoid, 12-18 x 6-10 µm. Thallus: C+ pink, K-, Pd-, occasionally, but more uncommon: C- or C+ pink, K- or K+ yellow > red, Pd- or Pd+ yellow (these different chemical reactions may result from interactions with remains of host thallus). Photobiont: Chlorococoid. Rare or understated, parasite of numerous crustose lichen species growing on well-lit siliceous rocks. N.B. Shares a similar as a small Placynthiella icmalea but the latter is never parasite. N.B. Non consensus has been reached concerning this species and various interpretations according to different authors are still found. Morphological traits highly variable according to the hosts.