Notes: crust lichen, on rock (not sandstone)
THALLUS: subsquamulose, areoles not overlapping, shiny, deep grayish brown, convex, K-, C-
MEDULLA: whitish, K-, C-
ALGAE: green, in a continuous layer
APOTHECIA: sunken, one per areole; epihymenium brown; hymenium clear; hypothecium clear, going quite deep; paraphyses simple, clear, gradually enlarging upward, 3.1+/-0.5 µm wide at base and 4.8+/-0.5 µm wide at tips; asci broadly clavate, walls and tip I+ very weak blue; all POL-, all K-
SPORES: many per ascus, clear, simple, round to oblong, (3.5)4.9+/-0.8(6.4) x (2.1)2.8+/-0.4(3.6) µm (N=27)

There are, alas, many brown Acarospora. This one is distinguished by being C-, having a continuous algal layer, spres 3-6 µm long, and relatively thick paraphyses (2.3-3 µm thick at base).