A lichen unusually coming from part of South America (7)
I believe the answer is:
chilean
'part of south america' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'a lichen unusually' is the wordplay.
'unusually' indicates anagramming the letters.
'a'+'lichen'='alichen'
'alichen' is an anagram of 'CHILEAN'.
'coming from' is the 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" .)