rose

Depressed women might not be able to smell them, but in ancient Rome, a wild rose would be placed on the door of a room where secret or confidential matters were discussed.
The phrase ‘sub rosa’ or ‘under the rose’, means to keep a secret – derived from this ancient Roman practice.

Paintings of roses on the ceilings of Roman banquet rooms were also a reminder that things said under the influence of wine (sub vino) should also remain ‘sub rosa’.