Primary thallus: squamulose to subfoliose, mat-forming, 1-4 cm wide, persistent; squamules: flattened, adnate on the substrate, upturned around edges, comparatively thick (300-1000 micro meter); lobes: 2-5 mm wide, margins subentire to crenate-lobate, fused, esorediate; upper side: greenish to olivaceous to copper to castaneous, often glossy and cracked; medulla: conspicuously white, with chalk-like structure (use razor blade!); lower side: cottony-fibrillose podetia: common but sometimes scarce even on well-developed thalli, dark brown to greenish brown, 0.5-1.5 cm tall, cup-forming; cups: 3-6 mm wide surface: corticate, areolate, verruculose, esorediate, microsquamulose (forming phyllidia with age) toward the base and also inside the cups Apothecia: fairly common on the podetia, up to 3 mm wide, brown ascospores: not observed Pycnidia: common on cup margins, pyriform, with hyaline gelatin conidia: 6-7 x 1 micro meter Spot tests: K- or K+ dingy yellowish, changing to brownish, C-, KC-, P+ red, UV- Secondary metabolite: fumarprotocetraric acid. Habitat and ecology: on thin soil or duff, sometimes over pebbles or muscicolous; calciphilous, mostly cold to temperate arid regions World distribution: on all continents Sonoran distribution: Arizona and Chihuahua. Notes: Cladonia pocillum is distinguished by thick, glossy, brown primary squamules, which are fused together, almost resembling a foliose lichen. The lower surface of the squamules is cottony. The short (< 1 cm) podetia with numerous peltate squamules on the insides of the cups also characterize this species. It is difficult to distinguish C. pocillum from depauperate collections of C. pyxidata. In montane localities C. chlorophaea may develop characters that resemble C. pocillum, particularly where the soredia have become corticate or where they have been shed. Specimens of C. fimbriata and C. chlorophaea from montane localities often consist of squamules only, which further confuses their identity. The specific status of C. pocillum is actually in doubt, because it is suspected to be only a sturdy morph of the C. pyxidata complex, that grows on base-rich soils and accumulates calcium oxalate. It may be an ecotype.