A new diterpenoid containing a rare carbobicyclic cembrane-derived skeleton, the capnosane skeleton, has been isolated from flowers of Greek tobacco. It has been identified as (1S*,3R*,4S*,6R*,7R*,8R*,11Z)-4,6,8-trihydroxy-11-capnosene- 2,10-dione by spectral methods and X-ray analysis of the corresponding benzoate. A full account of the X-ray work is given.