Away with you, nearly up-ending best flower (7)

I believe the answer is:

begonia

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'flower' is the definition.
(I know that Begonia is a type of flower)

I don't understand the remainder of the clue.

(Other definitions for begonia that I've seen before include "colourful flower" , "Common garden plant" , "Tropical plant" , "bloomer" , "Herbaceous plant whose flowers have no petals" .)

I've seen this clue in The Sun.

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