Plant's accountant seized by a US agency (6)
I believe the answer is:
acacia
'plant's' is the definition.
The answer is an example.
'accountant seized by a us agency' is the wordplay.
'accountant' becomes 'CA' (abbreviation for chartered accountant).
'seized by' indicates putting letters inside.
'us agency' becomes 'cia' (I've seen this before).
'a'+'cia'='acia'
'ca' inserted inside 'acia' is 'ACACIA'.
(Other definitions for acacia that I've seen before include "Australian tree" , "Plant like wattle" , "Flowering tree/shrub of Australia and Africa" , "Australian shrub" , "(Sub)tropical shrub with yellow or white flowers - wattle" .)