Runemark, H 1956: Studies in Rhizocarpon. I. Taxonomy of the yellow species in Europe. Opera Botanica 2(1): 1-152.

Thallus ca. 4 cm in diam. Areolae or groups of areolae dispersed on a well developed prothallus.

Areolae 0.4-1.5 mm in diam., 0.1-0.3 mm thick, +/- roundish to slightly angular, usually verrucose, slightly convex, faintly yellow to grayish-yellow, surface +/- smooth, matt; cortex ca. 20 u +/- indistinct; medulla white.

Apothecia 0.3-1.0 mm in diam., 0.2-0.5 mm thick, +/- roundish, strongly convex and without a margin (particulary old apothecia); sometimes in (sic) compound.  Cortex cells of excipulum +/- greenish, K+ more distinctly green.  Subhymenium dark brown, K-, usually 100-200 µ thick.  Hymenium 70-100 µ thick, colourless to faintly green, uppermost part dark green, K- or K+ more intensely green; apical cells of paraphyses roundish, opaque.  Epihymenium with dark, irregularly formed grains.  Asci clavate, 50-80 X 12-18 µ, containing 8 spores.  Spores uni-septate, 11-18 X 5-8 µ.

Lichen substances.  Probably rhizocarpic acid and norsitictic acid.  Reactions:  K+ blood-red, Pd+ yellow, I+ intensely blue. 

One collection examined.

Taxonomic remark.  Rh. dispersum is to a certain degree an intermediate species between the Alpicola and Superficiale Groups.  Morphologically and chemically it much resembles Rh. atroalbescens.  But the dark epihymenium, the roundish apical cells of the paraphyses, and the small spores make an inclusion of the species in the Superficiale Group natural.

Ecology. ?

Distribution.  Rh. dispersum is only known from the type locality in Spitsbergen.