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Unions oust leader, who is replaced with old plants (6)

Ross

I believe the answer is:

onions

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'plants' is the definition.
The answer is an example.

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(Other definitions for onions that I've seen before include "nuts" , "Famous lexicographer" , "If you know your vegetables, you're well up" , "Veg" , "Pungent, edible bulbs" .)

I've seen this clue in The Irish Times.
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