Flower with ultra-blue heads welcomed by Ophelia, for one (6)

I believe the answer is:

danube

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'flower' is the definition.
(Danube is an example)

I cannot understand how the rest of the clue works.

(Other definitions for danube that I've seen before include "flower" , "River flowing from Black Forest to Black Sea" , "5 down's river" , "Viennese river" , "It's blue according to the song" .)

I've seen this clue in the Irish Times (Crosaire) and the Irish Times.

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