Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.

Thallus: areolate-warty, rather thin, often bordered by a blackened base, sometimes obscurely lobed areoles: when still flat 0.5-0.8 mm in diam. surface: light gray or with slightly yellowish olive tinge, smooth and slightly shiny; cortex: leathery fertile verrucae: strongly convex, 1.1-1.6 mm across, often constricted at the base and almost peltate Apothecia: developing in older verrucae mazaedium: 0.20-0.35 mm in diam., flat to convex, black; thalline margin: thick, smooth cortex: consisting of three layers: the outermost one: hyaline, paraplectenchymatous, 813 µm; middle one: 25-55 µm, well delimited, with small, irregular crystals; innermost layer: very irregular and with prosoplectenchymatous hyphae penetrating deep into the medulla exciple: indistinct; hypothecium: light brown; central part of exciple 0.12-0.16 mm high, consisting of dark-colored hyphae hymenium: 70-90 µm tall asci: cylindrical, 33-38 x 5-6 µm when mature, 6-8 spored, with uniseriate spores ascospores: when mature non-septate, spherical, (9-)13-16(-17) µm, with a somewhat fine and irregular ornamentation; semi-mature spores: sometimes appearing faintly striate Pycnidia: immersed, spherical, 0.08-0.14 mm in diam., to elongated, black Spot tests: thallus: K-, C-, KC+ rose-red, P-; mazaedium: K+ red, P+ yellow to red Secondary metabolites: thallus containing 3-chlorodivaricatic acid; mazaedium containing norstictic and salazinic acids. Substrate and ecology: on rocks along the coast World distribution: Europe, Macaronesia, coastal California to British Columbia Sonoran distribution: southern California, Baja California, Baja California, and Sinaloa. Notes: See notes under T. santessonii for comparison of Thelomma mammosum with that species.