A US agency in power starts selling shrubs (7)

I believe the answer is:

acacias

I'm a little stuck... Click here to teach me more about this clue!

'shrubs' is the definition.
The answer and definition can be both plants as well as being plural nouns.
Maybe there's a link between them I don't understand?

'a us agency in power starts selling' is the wordplay.
'us agency' becomes 'cia' (I've seen this before).
'in' is an insertion indicator.
'power' becomes 'ac' (AC is an example).
'starts' suggests taking the first letters.
The first letter of 'selling' is 's'.
'a'+'cia'='acia'
'ac'+'s'='acs'
'acia' inserted into 'acs' is 'ACACIAS'.

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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