[Cladonia alcicornis var. firma Nyl., more, Cladonia foliacea var. firma (Nyl.) Vain., Cladonia nylanderi Cout., Cladonia nylanderi f. cervicorniformis Abbayes, Cladonia nylanderi f. lata Abbayes, Cladonia nylanderi f. nylanderi Cout., Cladonia nylanderi f. vulgaris Abbayes]
Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.
Primary thallus: squamulose, persistent, conspicuous; squamules: up to 25 mm long and 10 mm wide, glaucescent green to olivaceous above, bluish gray below (lobe tips: often white!), clearly thick (about 400 micro meter), irregularly crenate-lobate; lobe ends: strongly incurved podetia: very rare, up to 15 mm tall, cup-forming; cups: 2-4 mm wide, rarely proliferating from center surface: smoothly corticate to verruculose, esorediate, rarely squamulose, sometimes bearing abundant squamules along cup margins Apothecia: rare, 1-2.5 mm wide, dark brown ascospores: oblong-ellipsoid, 14-17 x 2-4 micro meter conidia: rare, not observed Spot tests: K+ yellow, C-, KC-, P+ red, UV- Secondary metabolites: atranorin and fumarprotocetraric acid Habitat and ecology: on soil, primarily in Mediterranean regions World distribution: Africa, Asia and Europe, western North America Sonoran distribution: not known from the area but occurring in adjacent California. Notes: Cladonia firma was discussed and first reported from North America in Hammer (1991). It is restricted to a few localities in San Luis Obispo Co., southern California, where it is locally abundant. It is expected to be more widespread because it is easily overlooked due to its poor production of podetia. It is distinguished by its large, thick squamules, which are green above, bluish below and contain atranorin (K+ yellow). The taxonomic status of the North American C. firma is somewhat uncertain.