Unions oust leader, who is replaced with old plants (6)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
onions
'plants' is the definition.
The answer is an example.
I don't understand the rest of the clue.
Can you help me to learn more?
(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" .)