Primary thallus: squamulose, evanescent; squamules: 1-4 mm long, up to 0.5 mm wide, digitately lobed, esorediate podetia: glaucescent to usually more or less brown, 30-70 mm tall, 1-2 mm wide, occasionally bearing many cups; cups: successsively proliferating from cup margins to produce new cups, with sieve-like perforations in the interiors; fertile podetia: more richly branching and without cups but producing many flattened branchlets with lateral slits surface: smoothly corticate to slightly areolate, often somewhat shiny, esorediate, somewhat squamulose Apothecia: common, numerous but small (up to 1 mm) at ends of the long, apical proliferations, dark brown ascospores: not observed Pycnidia: mainly produced on short teeth at cup margins, conical to subspherical, often somewhat constricted at base, with hyaline gelatin conidia: not observed Spot tests: K- or K+ yellowish changing to dingy brown, C-, KC-, P+ red, UV- Secondary metabolites: fumarprotocetraric acid and occasionally accessory ursolic acid. World distribution: North America, mainly eastern, extending along Rocky Mountains south to Coahuila, Mexico, but not to the west coast, essentially boreal Sonoran distribution: rare, in spruce-fir forest in eastern Arizona. Notes: This species is easily recognized by its unique sieve-like cups. However, it is often only seen in fertile state, when no cups are present, and then it is extremely similar to some morphs of Cladonia furcata. The main axes of fertile C. multiformis are largely flattened in cross-section, while in C. furcata they are invariably round. The ranges of the two species hardly overlap in western North America.