Thallus: crustose, effuse upper surface: white, 0.1-0.3 mm cortex: 10 µm thick, sometimes poorly developed medulla: white Ascomata: sometimes slightly undulating, sessile, 0.2-1 mm diam.; disc: convex, strongly white pruinose; exciple: protruding above the disc, with cortex and algae but sometimes without cortex; proper exciple: thin; epithecium: 10-20 µm thick, light brown to brown; hymenium: 60-70 µm high; paraphysoids: sparsely branched, parallel, hyaline, c. 1 µm in diam. asci: clavate, 50-60 x 10-15 µm, 8-spored ascospores: 13-15 x 3-4 µm Pycnidia: 0.1 mm diam conidia: bacilliform, 2-4 x 1-2 µm Spot tests: thallus K- or yellowish, C-, KC-, P+ yellow Secondary metabolite: psoromic acid. Substrate and ecology: growing on the trunks of trees and shrubs, such as Quercus, Heteromeles, Adenostoma, and Pinus but it is also lignicolous and often found on fence poles or unpainted wood, very rarely on rocks World distribution: distributed in coastal regions from southern Oregon southwards to northern Baja California Sonoran distribution: southern California.