Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.

photobiont: primary one a protococcoid green alga, secondary one absent conidia: hyaline, rather long, filiform or narrowly falcate, often bent Geography: temperate regions of Europe, Asia, North America, and New Zealand Substrate: usually on hard, weathered wood, or rarely bark. Etymology: The species epithet refers to the thick [crassus in Latin] thallus. areoles: +contiguous, subangular to +round, 0.3-0.7 mm across, +plane soredia: absent goniocysts: sparse or absent cortex: brown at surface, hyaline below, indistinct medulla: with occasional very coarse (15-20 µm across) hyaline crystals insoluble in K; photobiont: +irregularly scattered margin: concolorous with disc, inconspicuous Spot tests: apothecia and thallus K-, P- Substrate and ecology: on rotten wood, growing with X. vitiligo, in spruce-fir communities World and Sonoran distribution: Arizona, 2800 m.