Possible Clues:

• Shrub, wattle
• Bill joins a spy organisation as a plant
• Tropical shrub two aircraftmen observed way back
• Plant spies on an accountant
• This may blooming well turn first-rate for a couple of accountants (6)
• After a century, a tree comes to a finish of intelligence
• Twice a century it starts to grow into a tree
• Wattle that grows very well, coming up on two bills
• How an accountant may get planted on american intelligence
• Garden shrub