Leaves old politician out of stuff (5)

I believe the answer is:

cress

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'leaves' is the definition.
(I know that cress is a type of salad green)

I don't understand the rest of the clue.

(Other definitions for cress that I've seen before include "Salad plant paired with mustard" , "Salad sprouts" , "Salad vegetable" , "Cruciferous salad plant" , "Food item" .)

I've seen this clue in The Guardian.

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