Plant coming from Cuba is so unusual (8)
I believe the answer is:
scabious
'plant' is the definition.
'cuba is so unusual' is the wordplay.
'unusual' indicates anagramming the letters.
'cuba'+'is'+'so'='cubaisso'
'cubaisso' is an anagram of 'SCABIOUS'.
'coming from' acts as a link.
(Other definitions for scabious that I've seen before include "bloomer" , "Bluish purple flower" , "Casio bus (anag) - plant" , "Wild flower" , "One blooming" .)