Thallus: pendent to subpendent, 5-10 (-15) cm long, very brittle (fragmenting in herbarium packets) branching: irregular, isotomic to anisotomic dichotomous, frequent from the base; axils: usually acute branches: most c. 0.1 mm diam.; main branches (and basal ones, Sonoran material): 0.1-0.25 (-0.3) mm diam., sometimes becoming compressed toward the base, but straight, neither contorted nor foveolate surface: brown-black or olive blackish or black, usually concolorous and dull; lacking pseudocyphellae and true lateral spinules; soralia: sparse to abundant, fissural, mostly rather inconspicuous in Sonoran material, white or often speckled with black, up to 0.3 mm long Apothecia and Pycnidia: not seen in North American material Spot tests: cortex and medulla: K-, C-, KC-, UV-, P-; soralia: P+ orange or red Secondary metabolites: fumarprotocetraric acid (and protocetraric acid). Substrate and ecology: usually on conifers World distribution: circumboreal in the Northern Hemisphere; reports from Algeria and Mexico are dubious Sonoran distribution: common in Arizona, usually on Picea engelmannii or Abies lasiocarpa in forests at 2900-3400 m. Notes: As presently circumscribed this species is often very difficult to distinguish from B. fuscescens, with which it is often closely entangled. At least in populations from northern areas, B. lanestris characteristically is very unevenly thickened and has quite brittle branches with strictly fissural soralia, that are frequently larger than the branch diameter and is often black-spotted. However, in Sonoran populations the consistently thinner branches and the often dull, uniformly dark olive-blackish surface (without paler basal parts) seem to be the most consistent distinguishing features of B. lanestris. Another frequent difference between B. lanestris and B. fuscescens is that in B. lanestris the axils are acute even at the base, such that the branches tend to lie mostly parallel to each other and form narrow (c. 3 mm across) strands.