Tangelo variety in plain mentioned (4)
I believe the answer is:
ugli
'tangelo variety' is the definition.
(I've seen this in another clue)
'plain mentioned' is the wordplay.
'plain' becomes 'ugly' (I've seen this before).
'mentioned' indicates a 'sounds like' (homophone) clue.
'ugly' sounds like 'UGLI'.
'in' is the link.
(Other definitions for ugli that I've seen before include "Citrus fruit cross (which sounds offensive!)" , "West Indian citrus fruit" , "Trademarked hybrid citrus fruit" , "mixed fruit" , "Citrus fruit of the West Indies" .)