A number of sailors in charge of a plant (6)
I believe the answer is:
arnica
'plant' is the definition.
(arnica is a kind of plant)
'a number of sailors in charge of a' is the wordplay.
'number of sailors' becomes 'RN' (Royal Navy).
'in charge of' becomes 'ic'.
'a'+'rn'+'ic'+'a'='ARNICA'
(Other definitions for arnica that I've seen before include "flowering plant" , "Tincture for treating bruises" , "Herb used for treating bruises" , "something to treat bruises" , "Treatment for bruises" .)