Because of the yellowish color, it would go to one of the "Flavo-" genera, and because you are right about the white marks (pseudocyphellae) on the upper surface, that would make it Flavopunctelia.
JJ Johnson
2015-08-29
2015-08-29
United States of America, California, Point Reyes Petaluma Rd, CA
on trunk of tree K+ yellow, KC+ had some hints of red, C- bright green upper surface, brown lower surface, abundant brown apothecia. pseudocyphallae (white cracks) on upper surface, some margins of lobes have soredia (?) Parmelia?