Bit of a bloomer by the boys (5)
I believe the answer is:
sepal
'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 leaf" , "Violet" , "Part of a flower - peals (anag)" , "Part of a flower casing" , "Part of a flowering plant" .)