German flower in Heidelberg (4)

I believe the answer is:

elbe

I'm a little stuck... Click here to teach me more about this clue!

'german flower' is the definition.
'elbe' can be an answer for 'flower' (river in Germany). I'm not certain of the 'german' bit.

'in heidelberg' is the wordplay.
'in' indicates a hidden word.
'ELBE' can be found hidden inside 'heidelberg'.

Can you help me to learn more?

(Other definitions for elbe that I've seen before include "German banker" , "It flows through Germany" , "Current" , "Dresden and Hamburg's river" , "River rising in the Czech Republic and flowing into the North Sea" .)

I've seen this clue in The Sun.

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