Primary thallus: squamulose, persistent; squamules: 2-4 mm wide, ascendent podetia: 4-10 mm tall, whitish-gray, cup-forming; cups: 2-5 mm wide; margin: subentire, not proliferating in sterile state surface: esorediate, densely granulose (to schizidiose), corticate at base Apothecia: rare, dark brown ascospores: not seen Pycnidia: scarce, on cup margins conidia: not seen Spot tests: K-, C-, KC-, P+ red, UV- Secondary metabolites: fumarprotocetraric acid, trace amounts of protocetraric and confumarprotocetraric acids, traces of three unknown substances. Habitat and ecology: on earthen banks in arid lowland regions World distribution: western North America Sonoran distribution: Baja California and southern California. Notes: Cladonia hammeri resembles C. humilis, but it is not sorediate and not as distinctly corticate. We initially placed it in C. kurokawae Ahti & S. Stenroos, a similar granulose species with atranorin, which is known from Japan and China. However, a well-developed cortex is found on the podetia of C. kurokawae, and it extends higher up. Cladonia kurokawae is frequently fertile, with many proliferations arising from the cup margins. Cladonia pulvinella, another similar species, contains atranorin and bourgeanic acid and the cup margins are irregularly dentate and proliferating.