It grows in open country (5)

I believe the answer is:

heath

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'open country' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

(Other definitions for heath that I've seen before include "Former British PM" , "Scrubland" , "Edward -, former PM" , "Tract of open land" , "Ex-Tory PM" .)

I've seen this clue in the Evening Standard.

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