Growing source of a bit of a smell, possibly? (4)

I believe the answer is:

elms

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If this is the answer I cannot explain how the clue works.

(Other definitions for elms that I've seen before include "Deciduous trees with rough serrated leaves" , "Trees (of late, prone to disease)" , "Trees sound like Cockney steering devices" , "rugged feature of country churchyard" , "may have many leaves" .)

I've seen this clue in the Evening Standard.

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