Flower part pales strangely (5)
I believe the answer is:
sepal
'flower part' is the definition.
(I know that sepal is part of calyx)
'pales strangely' is the wordplay.
'strangely' indicates an anagram.
'pales' is an anagram of 'SEPAL'.
(Other definitions for sepal that I've seen before include "flowery bit" , "part of leaf" , "Enclosing part of flower" , "bit of a bloomer" , "Part of a flower casing" .)