Type of forest in Iran? (4)

I believe the answer is:

rain

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

'type of forest' is the definition.
(I've seen this in another clue)

'iran?' is the wordplay.
'iran' can be anagrammed to 'RAIN'.
However, I am not clear how the anagram is indicated.

'in' acts as a link.

Can you help me to learn more?

(Other definitions for rain that I've seen before include "Falling water" , "Fall in large quantities" , "Wet weather" , "downfall?" , "Storm" .)

I've seen this clue in the Evening Standard.

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