A flower instead of a half of bitter (5)

I believe the answer is:

aster

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'a flower' is the definition.
(type of flower)

'instead of a half of bitter' is the wordplay.
'instead of' becomes 'as' (I am not sure about this - if you are sure you should believe this answer much more).
'a half of' indicates taking half.
'bitter' halved is 'ter'.
'as'+'ter'='ASTER'

Can you help me to learn more?

(Other definitions for aster that I've seen before include "Plant like a Michaelmas daisy" , "bloomer" , "Flowering plant; tares (anag.)" , "Daisy-like garden flower" , "Flower of the daisy family - rates (anag)" .)

I've seen this clue in the Evening Standard.

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