Thallus: thin, light gray, consisting of small granules 0.04 granules: consist of a few to several hundreds of algal cells enclosed in the loose hyphal web of the mycobiont and interspersed by small, colorless, irregular crystals; in older parts, and particularly at the base of the stalks, sometimes fusing to form bigger, rather smooth, +pale brown verrucae with scattered small granules on the surface photobiont: a trebouxioid green alga Apothecia: slender, (0.6-)0.8-1.3(1.8) mm tall, 13-22 times as long as the width of the stalk stalk: long and slender, (0.04-)0.05-0.07(-0.08) mm in diam., a little thickened towards the capitulum; lower part: not pruinose, shining black, upper part +covered by a light greenish yellow pruina capitulum: (0.18-)0.22-0.30(0.42) mm in diam., depressed obovoid to lenticular, with a dense, greenish yellow pruina on the lower side exciple: well developed, broadly cup-shaped, 16-27 µm thick at the edge; hypothecium: lenticular, with convex upper surface, inconspicuous, pale brownish yellow, c. 30 µm thick and not distinctly limited from the exciple mazaedium: light brown; asci formed from ascogenous hyphae provided with hooks and mostly carrying 2-3 asci each asci: cylindrical, 20-28 x 2-3 µm, long-stalked, 8-spored, bursting when they are about 26-28 µm long, with uniseriate spores ascospores: spherical, (4.5-)6-7.3(-8.7) µm in diam., surface becoming irregularly reticulately fissured, with coarse cracks forming irregular polygonal areas Spot tests: thallus K-, C-, KC-, P- Secondary metabolites: vulpinic acid in the yellow pruina of the apothecia. Substrate and ecology: usually on bark of Picea or Thuja, near the base of old trees in shady and moist positions, rarely on lignum, in old coniferous forests World distribution: boreal zones of Europe and western North America (primarily west of the Rocky Mountains) Sonoran distribution: California. Notes: Chaenotheca subroscida is characterized by the greenish yellow pruina of its apothecia together with the gray, minutely granular thallus, that has a sorediate appearance. It differs from the closely related C. phaeocephala in its peculiar thallus and more slender apothecia, and also in ecology, as it almost exclusively occurs on bark of conifers and its distribution. See also Tibell and Beck (2002).