US ran a CIA operation, code named 'she-oak' (9)

I believe the answer is:

casuarina

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'named she-oak' is the definition.
The definition and answer can be both plants as well as being singular nouns.
Maybe they are linked in a way I don't understand?

'us ran a cia operation code' is the wordplay.
'us ran a cia' can be anagrammed to 'CASUARINA'.
But, I am not clear how this is indicated.

Can you help me to learn more?

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

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