Cladonia trassii was formally described as a new species in 1998 by Finnish lichenologist Teuvo Ahti.

The species epithet trassii honours Estonian lichenologist Hans Trass.

Ahti notes that the taxon is a new name for a species that Edvard Vainio originally called Cladonia cerasphora in 1894 and 1922 publications.

The expected results of standard chemical spot tests are PD+ (red), and K+ (yellow).

Documented collection locations include Khabarovsk Krai, Russian Far East; Alaska, United States; Northwest Territories and Québec, Canada; and Greenland.