Distribution: N - Lomb (S-F146634). C - Tosc, Laz, Sar. S - Pugl (Nimis & Tretiach 1999), Cal (Puntillo 1996), Si (Nimis & al. 1996b).
Description: Thallus small-foliose to squamulose-umbilicate, gelatinous when wet, black, usually smooth, sometimes becoming uneven, the squamules 10-15(-20) mm wide, forming rosettes or cushions, at first flat and lobulate, soon becoming divided into erect, adpressed or ascending, 2-4 mm wide and 0.4-0.8 mm thick lobes with a narrow base, rounded tips, and down-turned margins; lower surface attached by a central holdfast. Thallus 0.6-0.8 mm thick, the outer part formed by short-celled, 1.5-2.5 µm thick, mainly anticlinally oriented hyphae enclosing the photobiont cells, the medullary part of loosely arranged, 1-1.5 µm thick hyphae with cylindrical cells, lacking photobionts. Apothecia thallinocarps, sunken in thallus and difficult to recognize unless when wet, marginal to submarginal, filling the entire lobe tip, 2-4(-6) mm across, round to irregularly shaped, with a slightly flat to convex, dotted or fissured disc, and a 50-100 µm thick thalline margin. Proper exciple indistinct; epithecium brownish, 20-30 µm high; hymenium 80-100 µm high, finally incompletely separated into partial hymenia by intrusions of wedge-shaped, sterile thalline tissue, covered by a continuous layer of sterile tissue separated only by the pore-like discs of the partial hymenia, I+ blue turning wine-red; paraphyses short-celled, 2-3 µm thick, not or only slightly capitate; subhymenium compact, 30-40 µm high. Asci 16-32-spored, with a thin, one-layered, non-amyloid wall, an amyloid external apical cap, and passive spore discharge via apical rupturing. Ascospores 1-celled, hyaline, broadly ellipsoid, 5-9 x 3-5 µm. Pycnidia globose to broadly pyriform, immersed, unilocular, up to 0.2 mm wide. Conidia ellipsoid, 2-3 x 1-1.5 µm. Photobiont cyanobacterial, chroococcoid, with a few cells measuring 5-9 x 3-5 µm, penetrated by haustoria and surrounded by a brownish gelatinous sheath. Spot test: all negative. Chemistry: without lichen substances.
Note: on steeply inclined to vertical seepage tracks of more or less calcareous or basic siliceous rocks, most common in the Mediterranean belt. Most of the records of L. nigritella reported by Nimis from southern Italy (1993: 422) belong here.