Extract nitrogen from wild plant (6)

I believe the answer is:

violet

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

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

(Other definitions for violet that I've seen before include "Colour; flower, source of fragrance" , "Rainbow colour; flower" , "Purplish colour" , "Bluish-purple colour as of pretty flower" , "Girl's name - colour" .)

I've seen this clue in The Irish Times.

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