Primary thallus: squamulose, persistent; squamules: 1-4 mm wide, ascendent or adnate podetia: 4-10 mm tall, whitish-gray, simple, cup-forming; cups: 2-4 mm wide surface: clearly sorediate almost throughout (but in part disintegrating with age); soredia: fine to somewhat coarse; cortex: absent or very scarce at base ascospores: not seen Pycnidia: along margins of cup, spherical, blackish subglobose, with hyaline gelatin conidia: not observed Spot tests: K+ yellow, C-, KC-, P+ red, UV- Secondary metabolites: atranorin and fumarprotocetraric acid (with traces of protocetraric and confumarprotocetraric acids). Habitat and ecology: on earthen banks, mainly on mineral soil, arid lowland regions World distribution: North America (California and Mexico) Sonoran distribution: Baja California and southern California, especially the Channel Islands. Notes: Cladonia nashii resembles the atranorin chemotype of C. humilis, but it lacks the smooth cortex found on the podetia of C. humilis, and its soredia are slightly coarser. It is also similar to C. hammeri, which has a granular surface but which lacks distinct soredia. Cladonia hammeri also lacks atranorin. All three of these species can occur sympatrically in southern California.