1a Photobiont blue-green; thallus often < 1 cm wide
1b Photobiont green; thallus generally > 1 cm wide
2a Ascocarps forming perithecia (visible as black dots on the surface) or fruiting structures lacking; isidia and soredia lacking
3a Perithecia present
3b Perithecia lacking
4a Habitat usually semi-aquatic (streamside rocks, trickle lines on cliffs, seepy cracks in outcrops, etc.)
4b Habitat various but seldom semi-aquatic
2b Ascocarps forming apothecia; isidia or soredia occasionally present
5a Thallus white to gray, pruinose, appearing areolate, KC+R; apothecia brown, sunken in the thallus; spores minute, spherical, 2-4 μm diameter, many per ascus; on calcareous rock in continental climates
5b Thallus and apothecia otherwise; spores larger, 8/ascus
6a Thallus yellowish to greenish, occasionally whitish; apothecia lecanorine
6b Thallus brown, black, gray, whitish gray or red; apothecia lecideine
7a Upper surface conspicuously blistered or warty, the warts typically 1-5 mm diameter and 1 mm or more high; rare disjuncts
7b Upper surface variously textured (often rugose) but not conspicuously warty; common