Distribution: N - Ven, TAA, Lomb (Vezda Lich. Rar. Exs. 357), Piem (Isocrono & al. 2004, 2006), VA (Valcuvia 2000), Emil (Tretiach & al. 2008, Fariselli & al. 2020). C - Tosc (Tretiach & al. 2008, Lastrucci & al. 2009), Sar (Nöske 2000).
Description: Thallus minutely filamentous, black, forming 2-3(-5) cm wide, irregular carpets, consisting of soft, coarse, cylindrical, irregularly branched, smooth, decumbent filaments. Filaments >50 μm thick, to 200 μm thick at base, usually without spine-like branches, dark-green to brown when wet, black and somewhat shiny when dry, attached by a basal disc. Thallus (in section) ecorticate, the mycobiont cells loosely paraplectenchymatous, short-celled. Apothecia rare, inconspicuous, to 0.25 mm across, developing from pycnidia on swellings on the branches, with a punctiform, dark brown disc and an up to 40 μm wide thalline margin. Proper exciple well-developed, mostly colourless in lower part, brownish in upper part; epithecium brownish; hymenium colourless, gelatinous, I+ blue-green, K/I+ blue; paraphyses sparingly branched, the apices thickened; hypothecium colourless, dense. Asci 8.-spored, cylindrical-obclavate, thin-walled, with a K/I+ blue outer layer, without apical dome. Ascospores 1-celled (sometimes with 1-2 plasma bridges) hyaline, ellipsoid, 10-18(-20) × 3.5-6(-7) μm. Pycnidia rare, developing laterally from the filaments. Conidia hyaline, ellipsoid to bacilliform, 3-5 x 1-2 μm. Photobiont cyanobacterial (Stigonema), the photobiont trichomes with true branchings, i.e. side branchlets formed by periclinal cell divisions in the trichome, reacting I-. Spot tests: all negative. Chemistry: without lichen substances.
Note: an arctic-alpine to boreal-montane, circumpolar lichen with outliers in the cool-temperate zone, found on steeply inclined, periodically wetted or inundated siliceous rocks, on seepage tracks, etc., with optimum above treeline