Thallus: crustose, effuse and often widespreading, continuous, composed of small globose granules (goniocysyts), 12-40 µm in diam., thinly scattered or densely aggregated surface: pale to dark green to olivaceous-black; ecorticate, often with protruding hyphae Apothecia: sessile, 0.1-0.4 mm in diam. disc: whitish gray to dark gray, strongly convex, epruinose proper exciple: usually excluded, even in young apothecia epihymenium: hyaline, K-, or dull green and K+ violet hymenium: hyaline to dull straw colored, 25-45 µm tall; paraphyses: numerous, 1-1.5 µm wide, not capitate; hypothecium: hyaline to pale yellow, 40-170 µm thick asci: clavate, 26-40 x 8-12 µm, 8-spored cospores: hyaline, 0-1(-3) septate, often constricted at the septum, ellipsoid, 8-14 x 2.5-5 µm Pycnidia: often present, immersed to sessile, white to gray, 30-120 µm wide conidia: composed of two types: i) mesoconidia, simple, (3.5)-4.6 x 1.2-1.7 µm and ii) microconidia, simple, 5.5-8 x 0.7-1 µm Spot tests: K-, C- (but olivaceous pigment C+ violet, never red), KC-, P- Secondary metabolite: methoxymicareic acid. Substrate and ecology: usually on shaded tree boles, rarely on siliceous rocks World distribution: apparently widespread in Europe, in NE and SW North America, Tasmania and North Island of New Zealand Sonoran distribution: southern California (Santa Barbara Co.) and Arizona (Apache Co.). Notes: Exact distribution is uncertain because most records are included in M. prasina s. lat. The three chemical races of M. prasina Fr. have recently been recognized as distinct species, (c.f. Coppins 1983, van den Boom and Coppins 2001). The race containing methoxymicareic acid, which is by far the most frequent, is recognized as M. micrococca. Micarea prasina s. str., containing micareic acid, is an infrequent species of old-growth woodlands; whereas, the correct name for the third chemical race, which contains prasinic acid, is M. subviridescens (Nyl.) Hedl. The collection from Apache Co, Arizona has a thick, more continuous, dark green thallus that lacks secondary metabolites by TLC. Such collections are usually included in M. micrococca but their true affinity is uncertain. The microconidia occur in pycnidia at the smaller end of the range given.