Possible Clues:

• Chinese tree with aromatic bark — is a sac (anag)
• Plant producing dope occupying agency of spies
• The bark of spies infiltrated by a special police force in the past?
• Tree producing senna
• Plant with dope taken in by spies
• Plant enabling agents to capture idiot
• Spice Girl losing head is detained by spies
• Medicinal shrub with an aromatic bark
• Tree yielding a coarser kind of cinnamon
• Plant fool among those working in intelligence