Judas tree

The Judas tree was a tree from which a deadly poison could be extracted. Trained by the Silence, River Song kissed the Eleventh Doctor with lipstick made from the poison of the Judas tree. (TV: Let's Kill Hitler)
 * ''It is unknown if the poison could prevent a Time Lord from regenerating or if the Telesecta commented "Regeneration disabled" because the Doctor had run out his regenerative energy.