Thelomma
Crustose lichens containing a trebouxioid alga; thallus areolate, verrucose or somewhat lobate; apothecia mazaediate (with loose, soot-like spores amassed on the top), sunken in the thallus, the rim formed only of an exciple that is scarcely evident within the rim, but is thick and dark-pigmented below the hypothecium, the top of the apothecia ; hymenium formed of few, gnarled paraphyses, these hard to observe; hypothecium thick, dark brown or black; asci thin-walled, disintegrating before the spores mature; spores blackish brown at maturity, simple and spherical or elliptical and 1-septate, with ridges or cracks over the outer surface.
References: Tibell & Ryan 2004.
Thelomma ocellatum (Körber) Tibell
Thallus bullate-areolate, matte, light to medium grey with abundant globose black isidia on the tops of some of the areoles; apothecia occasional, 0.3-0.7 mm wide, with a sunken black rim and disc, mazaediate; spores 22-28 × 12-15 µ, finely ridged over the surface at maturity, 1-sepate, constricted at the septum.
Reactions: Medulla I+ dark blue.
Contents: Reported to sometimes have usnic acid, atranorin, or norstictic acid, and rhizocarpic acid and epanorin on the apothecia.
Habitat: On weathered wood in well lit, dry, well ventilated habitats, usually where enriched by bird excrement, lower to middle elevations.
Similar Species: Cyphelium inquinans has an exposed apothecial rim, usually with a ring of white pruina, and usually larger areoles.
Specimens: Goffinet 3768; G. Thor 8459.
Local Status: Uncommon.