Crossword Genius

Writer given one American plant (6)

Ross

I believe the answer is:

dahlia

'plant' is the definition.
(dahlia is a kind of plant)

'writer given one american' is the wordplay.
'writer' becomes 'dahl' (Roald Dahl).
'given' is a charade indicator (letters next to each other).
'one' becomes 'I' (Roman numeral).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'dahl'+'i'+'a'='DAHLIA'

(Other definitions for dahlia that I've seen before include "Showy garden flower" , "Plant with tuberous roots and showy coloured flower heads" , "Showy garden plant" , "Flower from tuber" , "In bed, root" .)

I've seen this clue in The Guardian.
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