Flower expert losing face (5)
I believe the answer is:
aster
'flower' is the definition.
(aster is a kind of flower)
'expert losing face' is the wordplay.
'expert' becomes 'master' (master is a kind of expert).
'losing face' means to remove the first letter.
'master' with its initial letter removed is 'ASTER'.
(Other definitions for aster that I've seen before include "Michaelmas daisy genus" , "Showy garden flower" , "Plant like a Michaelmas daisy" , "Flower of the daisy family - rates (anag)" , "(Starlike) flower" .)