Part of a calyx (5)
I believe the answer is:
sepal
'part of a calyx' is the definition.
('sepal' is part of 'calyx')
This is the entire clue.
(Other definitions for sepal that I've seen before include "Green part that forms a flower's calyx" , "Violet" , "bit of a bloomer" , "Part of a flower's outer envelope" , "Part of a flowering plant" .)