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

Apothecia: 0.6-1.8(-2.5) mm high stalk: 0.08-0.12 mm in diam., dull black with a coarsely granular surface, aeruginose in water mount, sometimes rather smooth and light grayish brown in very long-stalked apothecia; outer part: covered by groups of dark sclerotized hypahe; inner part: consisting of pale and rather straight, interwoven hyphae; hyphae: distinct capitulum: 0.14-0.28 mm in diam.; ascospore mass: dark brown or greenish black, not higher than width of head, epruinose; paraphyses: soon dissolving, not sclerotized exciple: in section reddish brown, well developed asci: broadly ellipsoid, when mature 9-11 x 5-6 µm ascospores: aeruginose, when mature 1-septate, 6.7-8.2 x 2.3-2.9 µm, distinctly ornamented with spiral ridges Pycnidia: absent Spot tests: exciple, stalk and ascospores K+ yellowish brown, N+ aeruginose. Substrate and ecology: on green algae (Stichococcus or others) or lichens (Psilolencia spp.), parasitic or commen salistic, on rocks, or roots, in shaded and humid localities, often under overhanging siliceous rocks World distribution: northern boreal to temperate zone in Eurasia and North America and also in New Zealand Sonoran distribution: California. Notes: Microcalicium arenarium much resembles M. ahlneri; see notes under that species. See Tibell (1997) for fuller description.