The new sesquiterpenoid 15-acetoxypinguisone has been found as the dominant constituent in the CDCl₃ extract of a specimen of the liverwort Cryptothallus mirabilis and the structure elucidated using ¹H and ¹³C NMR spectroscopy together with GC–MS and HRMS; a very minor constituent was assigned as (2S,6S)-cyclo-(7S)-cuparan-(3S)-ol, but the major/minor roles were reversed in a second specimen.