Plant’s account supported by a covert US group (6)
I believe the answer is:
acacia
'plant's' is the definition.
The answer is an example.
'account supported by a covert us group' is the wordplay.
'account' becomes 'ac' (abbreviation for account).
'supported by' means one lot of letters go next to another (in a down clue, some letters hold up others).
'covert us group' becomes 'CIA' (Central Intelligence Agency).
'ac'+'a'+'cia'='ACACIA'
(Other definitions for acacia that I've seen before include "Thorny flowering shrub" , "Flowering tree/shrub of Australia and Africa" , "Flowering tree or shrub" , "source of gum arabic" , "Plant such as the Australian wattle" .)