THALLUS: thin, smooth, whitish
APOTHECIA: thalline rims smooth, thick, even; disc pinkish, heavily pruinose
SPORES: 4 per ascus, large, hyaline, simple
CHEMISTRY: all C-
Smooth, thin, whitish crustose lichen, with big, beautiful donut-shaped, heavily-pruinose apothecia.
Bark.
No other genus has such thick, well-developed apothecial margins (see Lecanora, for example). Pertusaria also has large spores, but they are more thick-walled, often multi-layered.
Among Orcholechia, many look superficially similar, but chemistry separates it from most:
O. farinacea also C-, but has a thick, verrucose thallus O. juvenalis C+ red disc, thallus thick O. subathallina C+ red disc, thallus thin O. montana C+ pink/red rim, smaller apothecia O. subpallescens C+ pink/red rim, coastal O. oregonensis C+ pink/red rim, thallus also C+ red O. laevigata C+ pink/red rim, thallus C-, algal layer discontinuous O. trochophora C+ pink/red rim, thallus C-, algal layer continuous