Thallus: squamulose squamules: up to 0.7 mm diam., normally ascending and geotropically oriented, weakly to strongly convex upper surface: grayish green or greenish brown, dull; margin: crenulate, not upturned, concolorous with upper side soredia: green, farinose to granular, in labriform soralia upper cortex: up to 25 µm thick, composed of thin-walled hyphae Apothecia: up to 0.5 mm diam., marginal, plane; disc: black, epruinose, egyrose; margin: remaining prominent, entire or flexuose; exciple: composed of closely conglutinated hyphae, olivaceous in inner part, brownish black in the rim, not containing crystals, K+ brown, N- or N+ violet; hypothecium: dark brown; epithecium: dark brown, not containing crystals, K+ brown, N-; paraphyses: without swelling and pigment cap in apical cell asci: with a poorly developed tholus not containing visible structures, or remaining immature ascospores: broadly to narrowly ellipsoid, simple, 8-11.5 x 3-4.5 µm Pycnidia: sessile, black, attached marginally to the squamule conidia: bacilliform, 7-10 x c. 1 µm Spot tests: upper cortex K+ yellow, C+ red or C-, KC+ red or KC-, P+ yellow Secondary metabolites: thamnolic acid and often alectorialic acid. Substrate and ecology: on bark and wood of conifers (especially bark of Libocedrus and Sequoiadendron), often charred, in conifer forests at 1380-2160 m alt World and Sonoran distribution: North America, locally common in southern California and rare in Arizona. Notes: The species resembles H. scalaris morphologically, and the two species often grow in mosaics. Hypocenomyce sierrae differs in forming smaller, more green, and more crenulate squamules, in the secondary chemistry (thallus K+ yellow, P+ yellow), and in forming smaller, epruinose apothecia which often contain mature asci and spores. It is apparently more closely related to H. oligospora, but differs from that species in forming ascending, sorediate squamules.