Possible Clues:

• Flowering shrub a couple of accountants found around island
• Spiny tree or shrub with small yellow or white flowers
• Article about American spies in plant
• Mimosa family shrub
• A heartless organisation of people spying on agents leads to plant - a spiky type
• Tree or shrub, wattle
• Tree that's a favorite of giraffes
• Pea family shrub
• Plant a group of US agents to protect California
• Plant spies to pursue leaders of agitators, communists and anarchists