Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.
Life habit: lichenized Thallus: crustose, moderate to rather thick, verrucose, areolate or placodioid surface: gray to pale yellow or brown cortex: simple, c. 15 µm thick, formed by intertwined hyphae, or thicker, 25-45 µm, consisting of densely aggregated, anticlinal hyphae that form compacted strands penetrating deep into the medulla; hyphae: sometimes with swollen and brownish apices photobiont: primary one a Trebouxia species, secondary one absent Ascomata: apothecia sunken in projecting thallus warts, with well developed black mazaedium, 0.8-2.5 mm diam., about as high as wide proper exciple: reduced laterally, with very thin, hyaline margin, forming a basal collar at the edge of the hypothecium; hypothecium: dark brown to black, thick asci: cylindrical, formed singly, dissolving at an early stage ascospores: dark brown to black, simple and spherical or 1-septate and ellipsoid, with thick walls; ornamentation: minute to coarse, consisting of irregular ridges, faint parallel ridges or irregular cracks Conidiomata: coelomycetous (pycnidial), spherical to elongated, black.; mature pycnidia: with a single locule; ostiolum: dark, in the beginning punctiform, later irregularly split; pycnidium wall: poorly differentiated, outermost part of the pycnidium consisting of the radially arranged bases of the conidiophores surrounded by a few, hyaline enveloping hyphae, 1-1.5 µm in diam; conidiophores: branched, consisting of short cylindrical cells 4-5 x 2-3 µm, of Vobis' Type V; conidiogenous cells: both intercalarly and terminal conidia: formed on 1-2 µm long stalks, non-septate, hyaline, narrowly cylindrical, 3-4 x 1 µm Secondary metabolites: thallus with tetronic acid derivatives and usnic acid, rarely anthraquinones, orcinol depsidones and ß-orcinol depsidones; apothecia with ß-orcinol depsidones Substrate: on exposed faces of hard lime-free rock, or on wood Geography: Europe, Macaronesia and North America. Notes: Thelomma is characterized by the immersed ascomata with thin, pale lateral exciple and the large ascomata. Thelomma differs from Cyphelium in having its apothecia immersed in verrucae, with the lateral part of exciple very thin and hyaline, the basal part brown-black, very thick and cushion-like, and in most species non-septate spores. Both Cyphelium and Thelomma, however, are heterogeneous and not monophyletic in molecular phylogenies (unpublished). Reports of Cyphelium carolinianum (Tuck.) Zahlbr. (= Thelomma carolinianum (Tuck.) L. Tibell) from California (Hasse 1908a; Lindsay 1973) are based on misidentifications.