Lich. Fr. 3: [1] (1907).

Type locality: Data lacking.

Chemistry: Grayanic acid, TLC, Denmark (Aptroot 2000: 27).

Ecology: Similar to C. subulata and C. fimbriata but also on shady mossy rocks and on . Extremely rare in Germany (Wirth et al. 2013: 392).

Note: The species is not listed in Ahti (1993: 69), Aptroot (2000: 27) realized that C. callosa is an older name for C. fragilissima.