Possible Clues:

• Archaic lilac occasionally produces bush
• Plant in America around spies
• Common tree in Australian forests
• A heartless organisation of people spying on agents leads to plant - a spiky type
• Pharmaceutical thickener
• Article about CIA in plant
• Shrub known as wattle
• Spiny shrub with clusters of yellow or white flowers
• A cactus chopped in half, one by a shrub
• Article about Langley people in plant