It's a bit of a bloomer, boys! (5)

I believe the answer is:
sepal
'it's a bit of a bloomer' is the definition.
(part of a flower)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for sepal that I've seen before include "Part of a flowering plant" , "Part of the calyx of a flower" , "Enclosing part of flower" , "Part of a flower casing" , "flowery bit" .)
