A lichen unusually coming from part of South America (7)

I believe the answer is:

chilean

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'part of south america' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

'a lichen unusually' is the wordplay.
'unusually' indicates an anagram.
'a'+'lichen'='alichen'
'alichen' is an anagram of 'CHILEAN'.

'coming from' acts as a link.

Can you help me to learn more?

(Other definitions for chilean that I've seen before include "Santiago-born" , "Spanish speaker" , "Native of, eg, Santiago" , "Nationality of citizen of Santiago" , "foreign character" .)

I've seen this clue in The Times.

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