Animal back behind an opening plant (7)

I believe the answer is:

oregano

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'plant' is the definition.
(oregano is a kind of plant)

I don't understand the rest of the clue.

(Other definitions for oregano that I've seen before include "part of Mediterranean diet?" , "Dried marjoram" , "Marjoram-like herb" , "Gear Ono up for the herb" , "that's aromatic" .)

I've seen this clue in The Daily Express.

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