Is it lucky to have an extra leaf? (6)

I believe the answer is:

clover

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'leaf?' is the definition.
The definition and answer can be both plants as well as being singular nouns.
Maybe there's a link between them I don't understand?

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for clover that I've seen before include "Common trefoil" , "in which we can live luxuriously" , "Pea family plant with three-lobed leaves" , "Trifolium" , "Wild three-leafed plant" .)

I've seen this clue in the Evening Standard.

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